Transparent articles and face masks and associated treatments

Abstract

Transparent face masks, and associated treatments are generally provided. The transparent face masks provided herein may have a number of advantages, including improved visibility of a wearer's facial expressions, an improved ability to repel external fluids, an improved resistance to absorption of external fluids, and reduced damping of sound through the face mask. Associated treatment methods which can, in some embodiments, contribute to one or more of these benefits, are also provided.

Description

[0001] TRANSPARENT ARTICLES AND FACE MASKS AND ASSOCIATED

[0002] TREATMENTS

[0003] RELATED APPLICATIONS

[0004] This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 63 / 549,748, filed February 5, 2024, and entitled “TRANSPARENT ARTICLES AND FACE MASKS AND ASSOCIATED TREATMENTS,” which is incorporated herein by reference in its entirety for all purposes.

[0005] TECHNICAL FIELD

[0006] Transparent face masks, and associated treatments for improved comfort and functionality, are generally described.

[0007] BACKGROUND

[0008] Face masks are a widely used protective technology that filter air but that typically block a portion of a wearer’s face from view. Some people find the obstruction of the wearer’ s face unpleasant.

[0009] SUMMARY

[0010] Transparent face masks, and associated treatments are generally provided. The transparent face masks provided herein may have a number of advantages, including improved visibility of a wearer’s facial expressions, an improved ability to repel external fluids, an improved resistance to absorption of external fluids, and reduced damping of sound through the face mask. Associated treatment methods which can, in some embodiments, contribute to one or more of these benefits, are also provided. The subject matter of the present disclosure involves, in some cases, interrelated products, alternative solutions to a particular problem, and / or a plurality of different uses of one or more systems and / or articles.

[0011] In one aspect, a transparent face mask is provided. According to some embodiments, the transparent face mask, comprises: a first, support layer; a second, filtration layer adjacent to the first layer, wherein the second layer comprises a plurality of fibers having an average diameter of greater than or equal to 100 nm and less than or equal to 280 nm; and a third, support layer, situated such that the second layer is disposed between the first layer and the third layer; wherein the transparent face mask has an optical transparency of greater than or equal to 50% at a region of overlap between the first, second, and third layer, for a wavelength of light, wherein the wavelength of light is greater than or equal to 300 nm and less than or equal to 720 nm; and wherein a surface of the transparent face mask is hydrophobic.

[0012] In another aspect, a transparent face mask is provided. According to some embodiments, the transparent face mask, comprises: a first, support layer; a second, filtration layer adjacent to the first layer, wherein the second layer comprises a plurality of fibers having an average diameter of greater than or equal to 100 nm and less than or equal to 280 nm; and a third, support layer, situated such that the second layer is disposed between the first layer and the third layer; wherein the transparent face mask has an optical transparency of greater than or equal to 50% at a region of overlap between the first, second, and third layer, for a wavelength of light, wherein the wavelength of light is greater than or equal to 300 nm and less than or equal to 720 nm; and wherein a surface of the transparent face mask is hydrophilic.

[0013] In still another aspect, a transparent face mask is provided. According to some embodiments, the transparent face mask comprises: a first, support layer; and a second, filtration layer adjacent to the first layer, wherein the transparent face mask has an optical transparency to light at a wavelength of 300 nm to 720 nm of greater than or equal to 50% in at least a region of the face mask covering a mouth of a wearer when in use; and wherein the transparent face mask has only two pleats.

[0014] Other advantages and novel features of the present disclosure will become apparent from the following detailed description of various non-limiting embodiments of the disclosure when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and / or inconsistent disclosure, the present specification shall control.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Non-limiting embodiments of the present disclosure will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale unless otherwise indicated. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the disclosure shown where illustration is not necessary to allow those of ordinary skill in the art to understand the disclosure. In the figures:

[0017] FIGS. 1A-1C present schematic, cross-sectional illustrations of face masks, according to some embodiments;

[0018] FIGS 2A-2B provide schematic, cross-sectional illustrations of droplets contacting non-limiting face masks, according to some embodiments;

[0019] FIG. 3 provides a schematic, cross-sectional illustration of a method of forming a face mask comprising nanostructures, according to some embodiments;

[0020] FIG. 4 provides a schematic, cross-sectional illustration of a method of forming a face mask comprising nanostructures, according to some embodiments;

[0021] FIG. 5 presents the attenuation of sound by various face masks, according to some embodiments;

[0022] FIGS. 6A-6B present a variety of schematic illustrations of a non-limiting, two- pleated face mask, according to some embodiments;

[0023] FIG. 7 presents a photograph of a non-limiting two-pleated mask, contoured around a sculpted head, according to some embodiments;

[0024] FIG. 8 presents a photograph of a non-limiting pleat-roller, according to some embodiments; and

[0025] FIG. 9 presents dimensions of a non-limiting exemplary face mask having a design configuration according to the schematic illustration of FIG. 6A.

[0026] DETAILED DESCRIPTION

[0027] Transparent face masks represent a significant improvement in conventional face mask technology. However, improvements in transparency are often associated with significant reductions in filter-quality. Transparent face masks with high filtration efficiency are generally desired. The present disclosure is directed, in various aspects, towards transparent face masks with good mechanical and filtration properties. In some embodiments, the transparent face masks described herein possess hydrophobic and / or hydrophilic surfaces that can improve the comfort level of the masks and / or improve their safety.

[0028] According to one aspect, the disclosure is directed towards a face mask. The face mask may comprise one or more layers. The term “layer” generally refers to an arrangement of material that, when the material is laid flat, has a thickness dimension, a depth dimension that is perpendicular to the thickness dimension, and a width dimension that is perpendicular to both the thickness dimension and the depth dimension, where the lengths of each of the depth dimension and the width dimension are at least 3 times the length of the thickness dimension. In some embodiments, the length of the depth dimension of the layer is at least 5 times, at least 10 times, at least 25 times, at least 50 times, at least 100 times, at least 500 times, or at least 1000 times the length of the thickness dimension of the layer. In some embodiments, the length of the width dimension of the layer is at least 5 times, at least 10 times, at least 25 times, at least 50 times, at least 100 times, at least 500 times, or at least 1000 times the length of the thickness dimension of the layer. The width and depth dimensions of a layer define its major surfaces.

[0029] A face mask may comprise any appropriate number and configuration of layers. In some embodiments, the face mask comprises a first layer and a second layer adjacent to the first layer. In some embodiments, the second layer is a filtration layer of the face mask, which is configured to filter air passing through the face mask. The first layer may be a support layer that is configured to provide mechanical support to the filtration layer (e.g., the second layer).

[0030] According to some embodiments, the face mask further comprises a third layer (which may be, for example, another support layer). The second layer may be disposed between the first layer and the third layer. In some embodiments the second layer (e.g., the filtration layer) is disposed directly on the first, support layer. FIG. 1A presents such an embodiment, providing a cross-sectional, schematic illustration of face mask 101 comprising first layer 103, second layer 105 and third layer 107, where second layer 105 is disposed between first layer 103 and third layer 107. Such a “tri-layered” configuration of a face mask may be particularly advantageous, since it may provide mechanical support to the filtration layer (e.g., the second layer) on both sides while limiting overall mask thickness and permitting good air flow through the face mask. As shown in FIG. 1A, second layer 105 is directly adjacent to first layer 103.

[0031] According to some embodiments, the face mask further comprises a fourth layer (which may be, for example, another filtration layer). The fourth layer may be disposed between the first layer and the third layer. In some embodiments, the fourth layer (e.g., the filtration layer) is directly disposed on the third, support layer. FIG. IB presents such an embodiment, providing a cross-sectional, schematic illustration of face mask 101 comprising first layer 103, second layer 105, third layer 107, and fourth layer 109, where fourth layer 109 is disposed between first layer 103 and third layer 107. Such a “fourlayered” configuration of a face mask may be particularly advantageous for retaining transparency while reducing permeability to aqueous fluids such as blood. In some embodiments, the use of two or more filtration layers (e.g., a second, filtration layer and a fourth, filtration layer) may allow the two or more filtration layers to each be thinner, resulting in a face mask with improved safety and filtration properties for a given transparency. However, face masks comprising two or more filtration layers may be more difficult or costly to produce, meaning that face masks with only a single filtration layer may also be advantageous, depending on the embodiment.

[0032] According to some embodiments, a layer (e.g., a first layer, a second layer, a third layer, or a fourth layer) is or comprises a fiber web (a layer comprising a fiber web is interchangeably referred to as a “fiber web layer,” herein). For example, a layer may comprise a woven fiber web or a nonwoven fiber web. In some embodiments, the fiber web comprises a plurality of fibers. A plurality of fibers may be entangled (e.g., by weaving). The fibers may be continuous fibers or non-continuous fibers.

[0033] Although in some embodiments fiber web layers may be particularly useful, there are no particular limitations on the material of the layer and any of a variety of suitable materials may be used. As discussed below, in some embodiments, a face mask comprises a plurality of nanostructures deposited at a hydrophobic surface of a layer, as discussed below. The layer (and / or coating) and a plurality of nanostructures may have different compositions, in some embodiments. For example, the nanostructures may be formed from a relatively more hydrophobic material than a layer, or a coating on layer, in some embodiments. In one aspect, the disclosure is directed towards a transparent face mask. Without wishing to be bound by any particular theory, the light incident upon a conventional face mask is typically scattered by one or more layers of the conventional face mask, significantly limiting transmission of light through the face mask. The present disclosure has recognized that, without wishing to be bound by any particular theory, a high proportion of the scattered light is scattered from a filtration layer (e.g., a second layer, a fourth layer) of the face mask, and that this scattering could be limited by using a filtration layer (e.g., a second layer, a fourth layer) comprising fibers having a relatively small diameter. Without wishing to be bound by any particular theory, fibers having an average diameter smaller than a wavelength of visible light may have a reduced ability to scatter visible light, relative to wider fibers. Thus, according to some embodiments, the present disclosure is directed towards a face mask comprising a filtration layer (e.g., a second layer, a fourth layer) having a relatively small average fiber diameter, as discussed below.

[0034] A face mask described herein may have any of a variety of appropriate optical transparencies. In some embodiments, a face mask has an optical transparency of greater than or equal to 40%, greater than or equal to 45%, greater than or equal to 48%, greater than or equal to 50%, greater than or equal to 52%, greater than or equal to 55%, greater than or equal to 58%, greater than or equal to 60%, greater than or equal to 62%, greater than or equal to 65%, greater than or equal to 68%, greater than or equal to 70%, greater than or equal to 72%, greater than or equal to 75%, greater than or equal to 75%, or greater than or equal to 80% for a wavelength of light. In some embodiments, a face mask has an optical transparency of less than or equal to 80%, less than or equal to 78%, less than or equal to 75%, less than or equal to 72%, less than or equal to 70%, less than or equal to 68%, less than or equal to 65%, less than or equal to 62%, or less than or equal to 60% for a wavelength of light. Combinations of these ranges are also possible (e.g., greater than or equal to 40% and less than or equal to 80%, greater than or equal to 50% and less than or equal to 70%, or greater than or equal to 60% and less than or equal to 65%). Other ranges are also possible.

[0035] The aforementioned transparencies may be achieved using any of a variety of appropriate wavelengths of light. In some embodiments, a face mask has a transparency in an aforementioned range for light having a wavelength of greater than or equal to 190 nm, greater than or equal to 210 nm, greater than or equal to 240 nm, greater than or equal to 270 nm, greater than or equal to 300 nm, greater than or equal to 330 nm, greater than or equal to 360 nm, greater than or equal to 390 nm, greater than or equal to 420 nm, greater than or equal to 450 nm, greater than or equal to 480 nm, greater than or equal to 510 nm, greater than or equal to 540 nm, greater than or equal to 570 nm, greater than or equal to 600 nm, greater than or equal to 630 nm, greater than or equal to 660 nm, greater than or equal to 690 nm, or greater than or equal to 720 nm. In some embodiments, a face mask has a transparency in an aforementioned range for light having a wavelength of less than or equal to 810 nm, less than or equal to 780 nm, less than or equal to 750 nm, less than or equal to 720 nm, less than or equal to 690 nm, less than or equal to 660 nm, less than or equal to 630 nm, less than or equal to 600 nm, less than or equal to 570 nm, less than or equal to 540 nm, less than or equal to 510 nm, less than or equal to 480 nm, less than or equal to 450 nm, less than or equal to 420 nm, less than or equal to 390 nm, or less than or equal to 360 nm. Combinations of these ranges are also possible (e.g., greater than or equal to 190 nm and less than or equal to 810 nm). Other ranges are also possible.

[0036] In one particular set of embodiments, a transparency of greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, or greater than or equal to 80% may be achieved for a wavelength of greater than or equal to 300 nm and less than or equal to 720 nm.

[0037] A layer such as a filtration layer (e.g., a second layer, a fourth layer) may comprise a plurality of fibers. In some embodiments at least some of (e.g., all of) a plurality of fibers of a filtration layer (e.g., a second layer, a fourth layer) are polymeric fibers. Polymeric fibers of a filtration layer (e.g., a second layer, a fourth layer) may comprise PET, PLA, PLGA, PVDF, PHA, PHB, TPU, cellulose, poly(ethylene-co-vinyl acetate), polyurethane, polyvinylchloride, or combinations thereof.

[0038] For example, according to some embodiments, the polymeric fibers comprise a PVDF. The PVDF may be included in any of a variety of appropriate proportions versus the total weight of the polymeric fibers. For example, in some embodiments, the polymeric fibers comprise PVDF in an amount of greater than or equal to 75 wt%, greater than or equal to 80 wt%, greater than or equal to 85 wt%, greater than or equal to 90 wt%, greater than or equal to 95 wt%, or more. In some embodiments, the polymeric fibers comprise PVDF in an amount of less than or equal to 100 wt%, less than or equal to 95 wt%, less than or equal to 90 wt%, or less. For example, in some embodiments, the polymer composition comprises PVDF in an amount of greater than or equal to 75 wt% and less than or equal to 100 wt% (e.g., greater than or equal to 80 wt% and less than or equal to 90 wt%). Other amounts of PVDF inclusion in the polymeric fibers are also possible, as the disclosure is not so limited.

[0039] According to some embodiments, the polymeric fibers comprise a TPU. The TPU may be included in any of a variety of appropriate proportions versus the total weight of the polymeric fibers. For example, in some embodiments, the polymeric fibers comprise TPU in an amount of greater than or equal to 0 wt%, greater than or equal to 5 wt%, greater than or equal to 10 wt%, greater than or equal to 15 wt%, or more. In some embodiments, the polymeric fibers comprise TPU in an amount of less than or equal to 25 wt%, less than or equal to 20 wt%, less than or equal to 15 wt%, or less. For example, in some embodiments, the polymer composition comprises TPU in an amount of greater than or equal to 0 wt% and less than or equal to 25 wt% (e.g., greater than or equal to 10 wt% and less than or equal to 20 wt%). Other amounts of TPU inclusion in the polymeric fibers are also possible, as the disclosure is not so limited.

[0040] Combinations of the foregoing ranges are also possible. For example, in some embodiments, polymeric fibers comprise PVDF in an amount greater than or equal to 80 wt% and less than or equal to 90 wt% versus the total weight of the polymeric fibers, and further comprises TPU in an amount greater than or equal to 10 wt% and less than or equal to 20 wt% versus the total weight of the polymeric fibers. Such compositions may have advantageous properties for use in filtration layers. For example, in some embodiments the polymeric fibers are about 85 wt% PVDF and about 15 wt% TPU.

[0041] In some embodiments, natural fibers such as cotton fibers are used. In some embodiments, a plurality of fibers comprises a mixture of fibers with different compositions (e.g., a mixture of PLA fibers and PLGA fibers, or a mixture of cotton fibers and polymeric fibers). In some embodiments, a plurality of fibers comprises fibers with uniform compositions that are blends or copolymers of two or more polymers.

[0042] A filtration layer (e.g., a second layer, a fourth layer) may be made from compostable materials (e.g., PLA, PLGA), according to some embodiments. For example, a filtration layer (e.g., a second layer, a fourth layer) may be configured to break down over a period of less than or equal to 12 months, less than or equal to 10 months, less than or equal to 8 months, or less than or equal to 6 months, when composted.

[0043] Alternatively, in some embodiments, a filtration layer (e.g., a second layer, a fourth layer) may be made from recyclable materials. For example, in some embodiments, a filtration layer (e.g., a second layer, a fourth layer) comprises a vitrimer, which may be collected and re-processed (e.g., by dissolution in in mild solvents such as N-methyl pyrrolidone or dimethyl formamide or aqueous solution) for reuse. Exemplary vitrimers and / or other materials that may be used include, but are not limited to: epoxybased or vinyl-based vitrimers such as vanillin-based epoxy resins, vanillin-guaiacol resins (e.g., diglycidyl ether of bisphenol), and / or vitrimeric networks comprising guaiacol, eugenol, vanillic acid, isophoronediamine, epichlorohydrin, glycyrrhizic acid, soybean oil, poly(itaconate) elastomers, lignin-based vitrimers, polyimine-network based vitrimers, polybutadiene-based elastomers, succinic anhydride, glutaric anhydride, Methylhexahydrophthalic Anhydride (MHHPA), and / or phthalic anhydride .

[0044] In some embodiments, a filtration layer (e.g., a second layer, a fourth layer) may be formed by electrospinning (e.g., melt electrospinning or solvent electrospinning), and thus may comprise electospun fibers having the material types, dimensions, and amount described herein for the filtration layer (e.g., second layer, a fourth layer). As such, the filtration layer (e.g., second layer, fourth layer) may comprise continuous fibers.

[0045] The fibers of a filtration layer (e.g., a second layer, a fourth layer) may have any of a variety of appropriate diameters. As discussed above, in some embodiments, the diameters of the fibers are relatively small, with the advantageous effect of improving mask transparency. In some embodiments, the fibers of a filtration layer (e.g., a second layer, a fourth layer) have a diameter of less than or equal to 500 nm, less than or equal to 400 nm, less than or equal to 300 nm, less than or equal to 280 nm, less than or equal to 270 nm, less than or equal to 260 nm, less than or equal to 250 nm, less than or equal to 240 nm, less than or equal to 230 nm, less than or equal to 220 nm, less than or equal to 210 nm, less than or equal to 200 nm, less than or equal to 190 nm, less than or equal to 180 nm, less than or equal to 170 nm, less than or equal to 160 nm, less than or equal to 150 nm, less than or equal to 140 nm, less than or equal to 130 nm, less than or equal to 120 nm, or less than or equal to 110 nm. In some embodiments, the fibers of a filtration layer (e.g., a second layer, a fourth layer) have an average diameter of greater than or equal to 50 nm, greater than or equal to 60 nm, greater than or equal to 70 nm, greater than or equal to 80 nm, greater than or equal to 90 nm, greater than or equal to 100 nm, greater than or equal to 110 nm, greater than or equal to 120 nm, greater than or equal to 130 nm, greater than or equal to 140 nm, greater than or equal to 150 nm, greater than or equal to 160 nm, greater than or equal to 170 nm, greater than or equal to 180 nm, greater than or equal to 190 nm, greater than or equal to 200 nm, or greater than or equal to 210 nm. Combinations of these ranges are also possible (e.g., greater than or equal to 50 nm and less than or equal to 280 nm, greater than or equal to 100 nm and less than or equal to 200 nm, or greater than or equal to 200 nm and less than or equal to 280 nm). According to some embodiments, it has been observed that fibers with diameters larger than 100 nm, 120 nm, or 140 nm may be particularly useful in face masks, e.g., because they are less-flexible than smaller fibers. The reduced flexibility of fibers with diameters larger than 100 nm may increase the strength of the filtration layer (e.g., the second layer, a fourth layer) and reduce the need for techniques such as heating of the filtration layer, which may reduce transparency of a face mask. Other ranges are also possible.

[0046] Fibers may make up any of a variety of weight percentages of a filtration layer (e.g., a second layer, a fourth layer). In some embodiments, fibers make up greater than or equal to 50 wt%, greater than or equal to 55 wt%, greater than or equal to 60 wt%, greater than or equal to 65 wt%, greater than or equal to 70 wt%, greater than or equal to 75 wt%, greater than or equal to 80 wt%, greater than or equal to 85 wt%, or greater than or equal to 90 wt% of the filtration layer (e.g., the second layer, the fourth layer). In some embodiments, fibers make up less than or equal to 100 wt%, less than or equal to 95 wt%, less than or equal to 90 wt%, less than or equal to 85 wt%, less than or equal to 80 wt%, less than or equal to 75 wt%, less than or equal to 70 wt%, less than or equal to 65 wt%, less than or equal to 60 wt% of the filtration layer (e.g., the second layer, the fourth layer). Combinations of these ranges are also possible (e.g., greater than or equal to 50 wt% and less than or equal to 100 wt%, greater than or equal to 80 wt% and less than or equal to 100 wt%, or greater than or equal to 95 wt% and less than or equal to 100 wt% of the filtration layer (e.g., the second layer, the fourth layer)). Other ranges are also possible. A filtration layer (e.g., a second layer, a fourth layer) may have any of a variety of appropriate specific surface areas. In some embodiments, a filtration layer (e.g., a second layer, a fourth layer) has a specific surface area of greater than or equal to 1 m2 / g, greater than or equal to 2 m2 / g, greater than or equal to 3 m2 / g, greater than or equal to 4 m2 / g, greater than or equal to 5 m2 / g, greater than or equal to 6 m2 / g, greater than or equal to 7 m2 / g, greater than or equal to 8 m2 / g, greater than or equal to 9 m2 / g, greater than or equal to 10 m2 / g, greater than or equal to 11 m2 / g, greater than or equal to 12 m2 / g, greater than or equal to 13 m2 / g, greater than or equal to 14 m2 / g, greater than or equal to 15 m2 / g, greater than or equal to 16 m2 / g, greater than or equal to 17 m2 / g, greater than or equal to 18 m2 / g, greater than or equal to 19 m2 / g, greater than or equal to 20 m2 / g, greater than or equal to 21 m2 / g, greater than or equal to 21 m2 / g, greater than or equal to 21 m2 / g, or greater than or equal to 21 m2 / g. In some embodiments, a filtration layer (e.g., a second layer, a fourth layer) has a specific surface area of less than or equal to 35 m2 / g, less than or equal to 34 m2 / g, less than or equal to 33 m2 / g, less than or equal to 32 m2 / g, less than or equal to 31 m2 / g, less than or equal to 30 m2 / g, less than or equal to 29 m2 / g, less than or equal to 28 m2 / g, less than or equal to 27 m2 / g, less than or equal to 26 m2 / g, less than or equal to 25 m2 / g, less than or equal to 24 m2 / g, less than or equal to 23 m2 / g, less than or equal to 22 m2 / g, less than or equal to 21 m2 / g, less than or equal to 20 m2 / g, less than or equal to 19 m2 / g, less than or equal to 18 m2 / g, less than or equal to 17 m2 / g, less than or equal to 16 m2 / g, less than or equal to 15 m2 / g, less than or equal to 14 m2 / g, less than or equal to 13 m2 / g, less than or equal to 12 m2 / g, less than or equal to 11 m2 / g, less than or equal to 10 m2 / g, less than or equal to 9 m2 / g, less than or equal to 8 m2 / g, less than or equal to 7 m2 / g, or less than or equal to 6 m2 / g. Combinations of these ranges are also possible (e.g., greater than or equal to 1 m2 / g and less than or equal to 35 m2 / g, greater than or equal to 5 m2 / g and less than or equal to 25 m2 / g, greater than or equal to 10 m2 / g and less than or equal to 19 m2 / g, greater than or equal to 12 m2 / g and less than or equal to 18 m2 / g). Other ranges are also possible.

[0047] The specific surface area of a layer may be determined by Brunauer-Emmett- Teller (BET) analysis, specifically the ASTM D3663-20 test, according to some embodiments.

[0048] A filtration layer (e.g., a second layer, a fourth layer) described herein may have any suitable elastic modulus. In some embodiments, a filtration layer (e.g., a second layer, a fourth layer) layer has an elastic modulus of greater than or equal to 20 kPa, greater than or equal to 40 kPa, greater than or equal to 60 kPa, greater than or equal to 80 kPa, greater than or equal to 100 kPa, greater than or equal to 200 kPa, greater than or equal to 500 kPa, greater than or equal to 1 MPa, greater than or equal to 2 MPa, greater than or equal to 5 MPa, greater than or equal to 10 MPa, greater than or equal to 50 MPa, greater than or equal to 100 MPa, greater than or equal to 200 MPa, greater than or equal to 500 MPa, greater than or equal to 1 GPa, or greater than or equal to 2 GPa. In some embodiments, a filtration layer (e.g., a second layer, a fourth layer) has an elastic modulus of less than or equal to 5 GPa, less than or equal to 2 GPa, less than or equal to 1 GPa, less than or equal to 500 MPa, less than or equal to 200 MPa, less than or equal to 100 MPa, less than or equal to 50 MPa, less than or equal to 20 MPa, less than or equal to 10 MPa, less than or equal to 5 MPa, less than or equal to 2 MPa, less than or equal to 1 MPa, less than or equal to 500 kPa, less than or equal to 200 kPa, less than or equal to 100 kPa, less than or equal to 80 kPa, less than or equal to 60 kPa, or less than or equal to 40 kPa. Combinations of these ranges are also possible (e.g., greater than or equal to 20 kPa and less than or equal to 5 GPa, or greater than or equal to 20 kPa and less than or equal to 80 kPa). Other ranges are also possible.

[0049] The elastic modulus of a layer may be determined by nanoindentation followed by Oliver-Pharr analysis. Nanoindentation may be performed using a Nanovea indentation tester used to indent a layer or a layers using a Berkovich indenter tip, prior to Oliver-Pharr analysis. The indenter may have a contact load of 0.01-0.1 mN and a maximum load of 0.1-1 mN, such that the nanoindenter reaches a depth of less than or equal to 10% of the thickness of the layer.

[0050] A layer (e.g., a first layer, a third layer) such as a support layer may comprise a plurality of fibers. In some embodiments at least some of (e.g., all of) a plurality of fibers of a support layer (e.g., a first layer, a third layer) are polymeric fibers. In some embodiments at least some of (e.g., all of) a plurality of fibers of a support layer (e.g., a first layer, a third layer) are polymeric fibers. For example, a plurality of fibers may comprise nylon, cotton, polyester, copolyamides, a polyaramid (e.g., poly(meta-aramid), commercially known as Nomex; poly (para-aramid), commercially known as Kevlar), PET, PLA, PLGA, PVDF, PHA, PHB, TPU, cellulose, poly(ethylene-co-vinyl acetate), polyurethane, polyvinylchloride, or combinations thereof. In some embodiments, a plurality of fibers comprises a mixture of fibers with different compositions (e.g., a mixture of Nomex fibers and cotton fibers, or a mixture of cotton fibers and polymeric fibers). In some embodiments, a plurality of fibers comprises fibers with uniform compositions that are blends or copolymers of two or more polymers.

[0051] A support layer (e.g., a first layer, a third layer) may be made from compostable materials (e.g., PLA, PLGA), according to some embodiments. For example, a support layer may be configured to break down over a period of less than or equal to 12 months, less than or equal to 10 months, less than or equal to 8 months, or less than or equal to 6 months, when composted.

[0052] Alternatively, in some embodiments, a support layer (e.g., a first layer, a third layer) may be made from recyclable materials. For example, in some embodiments, a support layer (e.g., a first layer, a third layer) comprises a vitrimer, which may be collected and re-processed (e.g., by dissolution in an acid) for reuse.

[0053] Fibers of a support layer may be formed by any suitable process including, but not limited to, meltblowing and spunbond processes. In some embodiments, the fibres of the support layer are non-electrospun fibers.

[0054] A support layer (e.g., a first layer, a third layer) may comprise fibers having any of a variety of suitable diameters. In some embodiments, a support layer (e.g., a first layer, a third layer) comprises fibers having a diameter of greater than or equal to 0.5 microns, greater than or equal to 1 microns, greater than or equal to 2 microns, greater than or equal to 3 microns, greater than or equal to 4 microns, greater than or equal to 5 microns, greater than or equal to 6 microns, greater than or equal to 7 microns, greater than or equal to 8 microns, or greater than or equal to 9 microns. In some embodiments, a support layer (e.g., a first layer, a third layer) comprises fibers having a diameter of less than or equal to 10 microns, less than or equal to 9 microns, less than or equal to 8 microns, less than or equal to 7 microns, less than or equal to 6 microns, less than or equal to 5 microns, less than or equal to 4 microns, less than or equal to 3 microns, or less than or equal to 2 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.5 microns and less than or equal to 10 microns, greater than or equal to 1 microns and less than or equal to 5 microns, greater than or equal to 2 microns and less than or equal to 4 microns, or greater than or equal to 2 microns and less than or equal to 3 microns). Other ranges are also possible. Generally, the fibers of the support layer may have a larger average fiber diameter than those of the filtration layer (e.g., second layer, fourth layer).

[0055] Fibers of the support layer (e.g., the first layer, the third layer) may have any of a variety of appropriate lengths. In some embodiments, a support layer (e.g., a first layer, a third layer) comprises fibers having a length of greater than or equal to 0.1 cm, greater than or equal to 0.2 cm, greater than or equal to 0.5 cm, greater than or equal to 1 cm, greater than or equal to 2 cm, greater than or equal to 3 cm, greater than or equal to 4 cm, greater than or equal to 5 cm, greater than or equal to 6 cm, greater than or equal to 7 cm, greater than or equal to 8 cm, greater than or equal to 9 cm, greater than or equal to 10 cm, greater than or equal to 11 cm, greater than or equal to 12 cm, greater than or equal to 13 cm, greater than or equal to 14 cm, greater than or equal to 15 cm, greater than or equal to 16 cm, greater than or equal to 17 cm, greater than or equal to 18 cm, or greater than or equal to 19 cm. In some embodiments, a support layer (e.g., a first layer, a third layer) comprises fibers having a length of less than or equal to 20 cm, less than or equal to 19 cm, less than or equal to 18 cm, less than or equal to 17 cm, less than or equal to 16 cm, less than or equal to 15 cm, less than or equal to 14 cm, less than or equal to 13 cm, less than or equal to 12 cm, less than or equal to 11 cm, less than or equal to 10 cm, less than or equal to 9 cm, less than or equal to 8 cm, less than or equal to 7 cm, less than or equal to 6 cm, less than or equal to 5 cm, less than or equal to 4 cm, less than or equal to 3 cm, less than or equal to 2 cm, less than or equal to 1 cm, or less than or equal to 0.5 cm. Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 cm and less than or equal to 20 cm, greater than or equal to 1 cm and less than or equal to 12 cm, or greater than or equal to 3 cm and less than or equal to 7 cm). Other ranges are also possible. In some embodiments, continuous fibers are used.

[0056] Fibers may make up any of a variety of weight percentages of a support layer (e.g., a first layer, a third layer). In some embodiments, fibers make up greater than or equal to 0.1 wt%, greater than or equal to 0.25 wt%, greater than or equal to 0.5 wt%, greater than or equal to 1 wt%, greater than or equal to 2 wt%, greater than or equal to 5 wt%, greater than or equal to 8 wt%, greater than or equal to 10 wt%, greater than or equal to 12 wt%, greater than or equal to 15 wt%, greater than or equal to 18 wt%, greater than or equal to 20 wt%, greater than or equal to 25 wt%, greater than or equal to 30 wt%, greater than or equal to 35 wt%, greater than or equal to 40 wt%, greater than or equal to 45 wt%, greater than or equal to 50 wt%, greater than or equal to 55 wt%, greater than or equal to 60 wt%, greater than or equal to 65 wt%, greater than or equal to 70 wt%, greater than or equal to 75 wt%, greater than or equal to 80 wt%, greater than or equal to 85 wt%, or greater than or equal to 90 wt% of the support layer (e.g., the first layer, the third layer). In some embodiments, fibers make up less than or equal to 100 wt%, less than or equal to 95 wt%, less than or equal to 90 wt%, less than or equal to 85 wt%, less than or equal to 80 wt%, less than or equal to 75 wt%, less than or equal to 70 wt%, less than or equal to 65 wt%, less than or equal to 60 wt%, less than or equal to 55 wt%, less than or equal to 40 wt%, less than or equal to 35 wt%, less than or equal to 30 wt%, less than or equal to 25 wt%, less than or equal to 20 wt%, less than or equal to 18 wt%, less than or equal to 15 wt%, less than or equal to 12 wt%, less than or equal to 10 wt%, less than or equal to 8 wt%, or less than or equal to 5 wt% of the support layer (e.g., the first layer, the third layer). Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 wt% and less than or equal to 100 wt%, greater than or equal to 0.25 wt% and less than or equal to 25 wt%, or greater than or equal to 0.25 wt% and less than or equal to 5 wt%). Other ranges are also possible.

[0057] The support layer (e.g., the first layer, the third layer) may have any of a variety of appropriate specific surface areas. In some embodiments, a support layer (e.g., a first layer, a third layer) has a specific surface area of greater than or equal to 0.1 m2 / g, greater than or equal to 0.2 m2 / g, greater than or equal to 0.5 m2 / g, greater than or equal to 0.8 m2 / g, greater than or equal to 1 m2 / g, greater than or equal to 1.2 m2 / g, greater than or equal to 1.5 m2 / g, greater than or equal to l.m2 / g, greater than or equal to 2 m2 / g, greater than or equal to 3 m2 / g, or greater than or equal to 4 m2 / g. In some embodiments, a support layer (e.g., a first layer, a third layer) has a specific surface area of less than or equal to 5 m2 / g, less than or equal to 4 m2 / g, less than or equal to 3 m2 / g, less than or equal to 2 m2 / g, less than or equal to 1.8 m2 / g, less than or equal to 1.5 m2 / g, less than or equal to 1.2 m2 / g, less than or equal to 1 m2 / g, less than or equal to 0.8 m2 / g, less than or equal to 0.5 m2 / g, or less than or equal to 0.2 m2 / g. Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 m2 / g and less than or equal to 5 m2 / g, greater than or equal to 0.5 m2 / g and less than or equal to 2 m2 / g, or greater than or equal to 1 m2 / g and less than or equal to 1.5 m2 / g). Other ranges are also possible. A support layer (e.g., a first layer, a third layer) described herein may have any suitable elastic modulus. In some embodiments, a support layer (e.g., a first layer, a third layer) layer has an elastic modulus of greater than or equal to 30 kPa, greater than or equal to 40 kPa, greater than or equal to 60 kPa, greater than or equal to 80 kPa, greater than or equal to 100 kPa, greater than or equal to 200 kPa, greater than or equal to 500 kPa, greater than or equal to 1 MPa, greater than or equal to 2 MPa, greater than or equal to 5 MPa, greater than or equal to 10 MPa, greater than or equal to 50 MPa, greater than or equal to 100 MPa, greater than or equal to 200 MPa, greater than or equal to 500 MPa, greater than or equal to 1 GPa, greater than or equal to 2 GPa, greater than or equal to 2.5 GPa, greater than or equal to 3 GPa, greater than or equal to 3.5 GPa. In some embodiments, a support layer (e.g., a first layer, a third layer) has an elastic modulus of less than or equal to 9 GPa, less than or equal to 7 GPa, less than or equal to 5 GPa, less than or equal to 2 GPa, less than or equal to 1 GPa, less than or equal to 500 MPa, less than or equal to 200 MPa, less than or equal to 100 MPa, less than or equal to 50 MPa, less than or equal to 20 MPa, less than or equal to 10 MPa, less than or equal to 5 MPa, less than or equal to 2 MPa, less than or equal to 1 MPa, less than or equal to 500 kPa, less than or equal to 200 kPa, less than or equal to 100 kPa, less than or equal to 80 kPa, less than or equal to 60 kPa, or less than or equal to 40 kPa. Combinations of these ranges are also possible (e.g., greater than or equal to 30 kPa and less than or equal to 9 GPa, or greater than or equal to 30 kPa and less than or equal to 200 kPa). Other ranges are also possible.

[0058] A face mask may, in some embodiments, comprise one or more separation layers. A separation layer (e.g., a fifth layer) may be configured, according to some embodiments, such that it is disposed between and separates two other layers (e.g., a first layer, a second layer, a third layer, or a fourth layer) of the face mask. For example, a separation layer may be disposed between two filtration layers (e.g., between a second layer and a fourth layer) of a face mask. FIG. 1C presents such an embodiment, providing a cross-sectional, schematic illustration of face mask 101 comprising first, support layer 103, second, filtration layer 105, third, support layer 107, fourth, filtration layer 109, and fifth, separation layer 111, where separation layer 111 is disposed between second, filtration layer 105 and fourth, filtration layer 109. One or more separation layers may be used in a face mask, depending on the embodiment. According to some embodiments, the use of the separation layer is advantageous for reducing wear on a filtration layer of a face mask. For example, the separation layer may separate a second, filtration layer from a fourth, filtration layer, such that the second layer and the fourth layer are less prone to damage from their friction against one another.

[0059] A layer such as a separation layer (e.g., a fifth layer) may comprise a plurality of fibers. In some embodiments at least some of (e.g., all of) a plurality of fibers of a separation layer (e.g., a fifth layer) are polymeric fibers. In some embodiments at least some of (e.g., all of) a plurality of fibers of a separation layer (e.g., a fifth layer) are polymeric fibers. For example, a plurality of fibers may comprise nylon, cotton, polyester, copolyamides, a polyaramid (e.g., poly(meta-aramid), commercially known as Nomex; poly (para-aramid), commercially known as Kevlar), PET, PLA, PLGA, PVDF, PHA, PHB, TPU, cellulose, poly(ethylene-co-vinyl acetate), polyurethane, polyvinylchloride, or combinations thereof. In some embodiments, a plurality of fibers comprises a mixture of fibers with different compositions (e.g., a mixture of Nomex fibers and cotton fibers, or a mixture of cotton fibers and polymeric fibers). In some embodiments, a plurality of fibers comprises fibers with uniform compositions that are blends or copolymers of two or more polymers. According to some embodiments, a nylon separation layer has been observed to be advantageous for use as a separation layer.

[0060] Alternatively, in some embodiments, a separation layer (e.g., a fifth layer) may be made from recyclable materials. For example, in some embodiments, a separation layer (e.g., a fifth layer) comprises a vitrimer, which may be collected and re-processed (e.g., by dissolution in an acid) for reuse.

[0061] According to some embodiments, a separation layer comprises a fiber web. A separation layer may comprise fibers in any of a variety of appropriate proportions of the separation layer. In some embodiments, a separation layer comprises fibers in a weight percentage of greater than or equal to 0.1 wt%, greater than or equal to 1 wt%, greater than or equal to 2 wt%, greater than or equal to 5 wt%, greater than or equal to 10 wt%, greater than or equal to 20 wt%, greater than or equal to 30 wt%, greater than or equal to 40 wt%, greater than or equal to 50 wt%, greater than or equal to 60 wt%, greater than or equal to 70 wt%, greater than or equal to 80 wt%, greater than or equal to 90 wt%, greater than or equal to 95 wt%, or greater than or equal to 98 wt%. In some embodiments, a separation layer comprises fibers in a weight percentage of less than or equal to 100%, less than or equal to 99 wt%, less than or equal to 98 wt%, less than or equal to 95 wt%, less than or equal to 90 wt%, less than or equal to 80 wt%, less than or equal to 70 wt%, less than or equal to 60 wt%, less than or equal to 50 wt%, less than or equal to 40 wt%, less than or equal to 30 wt%, less than or equal to 20 wt%, less than or equal to 10 wt%, or less than or equal to 5 wt%. Combinations of these ranges are also possible (e.g., greater than or equal to 0.1 wt% and less than or equal to 100 wt%, greater than or equal to 95 wt% and less than or equal to 99 wt%, or greater than or equal to 98 wt% and less than or equal to 99 wt%). Other ranges are also possible.

[0062] A separation layer may include fibers having any of a variety of appropriate diameters. In some embodiments, a separation layer includes fibers having an average diameter of greater than or equal to 1 micron, greater than or equal to 2 microns, greater than or equal to 5 microns, greater than or equal to 10 microns, greater than or equal to 15 microns, greater than or equal to 20 microns, greater than or equal to 25 microns, greater than or equal to 30 microns, greater than or equal to 35 microns, greater than or equal to 40 microns, greater than or equal to 45 microns, greater than or equal to 50 microns, greater than or equal to 55 microns, greater than or equal to 60 microns, greater than or equal to 65 microns, greater than or equal to 70 microns, greater than or equal to 75 microns, greater than or equal to 80 microns, greater than or equal to 85 microns, greater than or equal to 90 microns, or greater than or equal to 95 microns. In some embodiments, a separation layer includes fibers having an average diameter of less than or equal to 100 microns, less than or equal to 95 microns, less than or equal to 90 microns, less than or equal to 85 microns, less than or equal to 80 microns, less than or equal to 75 microns, less than or equal to 70 microns, less than or equal to 65 microns, less than or equal to 60 microns, less than or equal to 55 microns, less than or equal to 50 microns, less than or equal to 45 microns, less than or equal to 40 microns, less than or equal to 35 microns, less than or equal to 30 microns, less than or equal to 25 microns, less than or equal to 20 microns, less than or equal to 15 microns, less than or equal to 10 microns, or less than or equal to 5 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 1 microns and less than or equal to 100 microns, greater than or equal to 5 microns and less than or equal to 20 microns, or greater than or equal to 10 microns and less than or equal to 15 microns). Other ranges are also possible.

[0063] A separation layer may include fibers having any of a variety of appropriate lengths. In some embodiments, a separation layer includes fibers having an average length of greater than or equal to 2.0 cm, greater than or equal to 2.5 cm, greater than or equal to 3.0 cm, greater than or equal to 3.5 cm, greater than or equal to 4.0 cm, greater than or equal to 4.5 cm, greater than or equal to 5.0 cm, greater than or equal to 5.5 cm, greater than or equal to 6.0 cm, greater than or equal to 6.5 cm, greater than or equal to 7.0 cm, greater than or equal to 7.5 cm, greater than or equal to 8.0 cm, greater than or equal to 8.5 cm, greater than or equal to 9.0 cm, greater than or equal to 9.5 cm, greater than or equal to 10 cm, greater than or equal to 10.5 cm, greater than or equal to 11.0 cm, greater than or equal to 11.5 cm, greater than or equal to 12 cm, greater than or equal to

[0064] 12.5 cm, greater than or equal to 13 cm, greater than or equal to 13.5 cm, greater than or equal to 14 cm, greater than or equal to 14.5 cm, greater than or equal to 15 cm, greater than or equal to 15.5 cm, greater than or equal to 16.0 cm, greater than or equal to 16.5 cm, greater than or equal to 17.0 cm, greater than or equal to 17.5 cm, greater than or equal to 18.0 cm, greater than or equal to 18.5 cm, greater than or equal to 19.0 cm, or greater than or equal to 19.0 cm. In some embodiments, a separation layer includes fibers having an average length of less than or equal to 20.0 cm, less than or equal to

[0065] 19.5 cm, less than or equal to 19.0 cm, less than or equal to 18.5 cm, less than or equal to

[0066] 18.0 cm, less than or equal to 17.5 cm, less than or equal to 17.0 cm, less than or equal to

[0067] 16.5 cm, less than or equal to 16.0 cm, less than or equal to 15.5 cm, less than or equal to

[0068] 15.0 cm, less than or equal to 14.5 cm, less than or equal to 14.0 cm, less than or equal to

[0069] 13.5 cm, less than or equal to 13.0 cm, less than or equal to 12.5 cm, less than or equal to

[0070] 12.0 cm, less than or equal to 11.5 cm, less than or equal to 11.0 cm, less than or equal to

[0071] 10.5 cm, less than or equal to 10.0 cm, less than or equal to 9.5 cm, less than or equal to 9.0 cm, less than or equal to 8.5 cm, less than or equal to 8.0 cm, less than or equal to 7.5 cm, less than or equal to 7.0, less than or equal to 6.5 cm, less than or equal to 6.0 cm, less than or equal to 5.0 cm, less than or equal to 4.5 cm, less than or equal to 4.0 cm, less than or equal to 3.5 cm, less than or equal to 3.0 cm, or less than or equal to 2.5 cm. Combinations of these ranges are also possible (e.g., greater than or equal to 2.0 cm and less than or equal to 20.0 cm, greater than or equal to 9.0 cm and less than or equal to 18.0 cm, or greater than or equal to 9.5 cm and less than or equal to 17.5 cm). Other ranges are also possible.

[0072] It should, of course, be understood that the mask may include one or more additional layers, in addition to support layers, filtration layers, and / or separation layers, as the disclosure is not so limited. For example, a face mask may comprise one or more layers of an adhesive, depending on the embodiment.

[0073] One or more surfaces of a face mask (e.g., a surface of a first layer, a surface of a third layer) may be treated, according to some embodiments, in order to control the interaction of the face mask with a fluid. For example, the surface may be treated by depositing a plurality of nanostructures, and / or a coating layer on the surface, as described in greater detail below. Such treatments can present significant advantages, depending on the embodiment. For example, face masks are commonly used in medical contexts, where potentially infectious fluids such as blood might contact an external surface of a face mask. In such contexts, it may be desirable for the face mask to include a hydrophobic (e.g., a superhydrophobic or oleophobic) external surface that can repel water. In contrast, it has been recognized that a common complaint about face masks is the discomfort associated with “misting” of an internal surface of a face mask during use. By treating an internal surface of a face mask to make it hydrophilic (as discussed in greater detail below), this problem may be avoided, improving comfort of the face mask for a wearer. Such treatments can, in some embodiments, have little to no impact on the transparency of the face mask.

[0074] Generally, internal and / or external surfaces of the face mask (e.g., inner most and / or outermost surfaces with respect to a user wearing the face mask, respectively) may be treated to make them hydrophobic or hydrophilic. For example, it may be particularly advantageous for a face mask to include both a hydrophobic external surface (e.g., outermost surface with respect to a user wearing the face mask) and a hydrophilic internal surface (e.g., inner most surface with respect to a user wearing the face mask), as described herein. However, other combinations (e.g., wherein an external surface and an internal surface are both hydrophobic or are both hydrophilic) are also possible, as the disclosure is not so limited.

[0075] In some embodiments, face masks comprising hydrophobic and / or oleophobic surfaces, and associated methods, are described. In some embodiments, the methods herein are directed towards the fabrication of non-fluorinated hydrophobic and / or oleophobic surfaces on face masks, which may provide a number of environmental and performance-related advantages. In a first aspect, a method of forming a face mask is generally described. A method may comprise forming one or more nanostructures at a surface of a layer (e.g., a support layer, such as a first layer or a third layer) such that the surface comprises the nanostructures. The layer may be a layer of a face mask, or a layer suitable for subsequent use in a face mask. Without wishing to be bound by any particular theory, the presence of nanostructures at a layer may produce a nanoscale texture that can improve the hydrophobicity and / or oleophobicity of a layer, relative to a layer comprising the same material without the nanostructures, all other factors being equal. For example, FIG. 2A provides a schematic cross-sectional illustration of a nonlimiting flat layer 201 in contact with a water droplet 203 to create a contact angle 205 defined by a direction 207 at which the surface of water droplet 203 contacts layer 201. The “contact angle” of a particular liquid phase (e.g., water) on a layer is measured through the bulk of the liquid phase. Generally, higher water contact angles are associated with more hydrophobic and / or oleophobic interfaces.

[0076] In contrast to FIG. 2A, FIG. 2B provides a cross-sectional, schematic illustration of a nonlimiting layer 202 comprising nanostructures 211. As shown in FIG 2B, a contact angle 205 between a water droplet 203 and a layer 202 is greater than the contact angle 205 shown in FIG. 2A as a result of the presence of nanostructures 211. Without wishing to be bound by any particular theory, the increase in contact angle resulting from the presence of nanostructures may be attributable to the presence of an ambient gas between nanostructures 211. An advantage of some methods described herein is the formation of such nanostructures on the surface of a layer (e.g., a layer suitable for use in a face mask, such as a first layer or a third layer), which has been difficult to achieve. It should be appreciated that while FIG. 2B shows nanostructures that are regularly sized and spaced, in other embodiments other shapes, sizes, and spacing of nanostructures are possible, as described in more detail herein. For instance, in some embodiments, heterogeneous nanostructures are formed (e.g., nanostructures having different heights, widths, diameters, and / or lengths, etc.).

[0077] In some embodiments, a method comprises forming nanostructures (e.g., at a surface of a face mask, or at a surface of a layer, such as a support layer that may be a assembled into a first layer or a third layer of a face mask) using a plasma. A method may comprise a first step of exposing a layer to a plasma. FIG. 3 presents a schematic illustration of a nonlimiting example of such a method. In a first method step 350, a layer 301 is exposed to a first plasma 320 to produce a plurality of nanostructures 307 at a surface of layer 301. According to some embodiments, the plasma may be used to chemically vapor deposit nanostructures at the surface of a layer (e.g., at a surface of a support layer that may be a first layer and / or a third layer of a face mask). Without wishing to be bound by any particular theory, in some embodiments, the nanostructures are formed by an island growth mechanism. As shown illustratively in FIG. 3, the resulting nanostructures may be discrete entities that are separated and isolated from other nanostructures (e.g., the nanostructures are unconnected from each other and / or are separated from each other by a material that is different from the material forming the nanostructures). As described herein and with respect to this figure, in some embodiments, nanostructures are formed using a top down approach that does not involve etching of a layer. In other words, the process lacks an etching step.

[0078] In some embodiments, the method shown in FIG. 3 may be used to form heterogeneous nanostructures (e.g., nanostructures having different heights, widths, diameters, and / or lengths, etc.). In some embodiments, the method may be used to form homogeneous nanostructures. In other embodiments, the method may be used to form heterogenous nanostructures.

[0079] A plurality of nanostructures may be formed at a surface of a layer (e.g., at a surface of a support layer that may be a first layer or a third layer) by exposing a surface of the layer to a plasma comprising a monomer. In some embodiments, exposing a surface of a layer to a plasma that comprises a monomer produces a face mask with a plurality of nanostructures at a surface of the layer. A plurality of nanostructures may comprise a polymer (e.g., a polymerized monomer of the monomers present in the plasma).

[0080] Any of a variety of suitable plasmas may be used to produce a plurality of nanostructures at a surface of a face mask. In some embodiments, a plasma may comprise a monomer. For example, a plasma may comprise an organic monomer, such as a hydrocarbon monomer. According to some embodiments, a method comprises polymerizing monomers (e.g., hydrocarbon monomers) from a plasma to form a polymer nanostructure during plasma deposition. A nanostructure formed by plasma deposition may be or comprise a polymerized form of a monomer in the plasma. Thus, an organic monomer such as a hydrocarbon monomer may be polymerized by the plasma to produce an organic polymer such as a hydrocarbon polymer. Methods disclosed herein may allow the formation of polymer nanostructures via an island growth mechanism that does not involve masking or patterning. Forming nanostructures by island growth may have any of a variety of advantages for producing hydrophobic and / or oleophobic coatings on layers. For example, island growth mechanisms may be scalable to large layer surfaces, and / or may be suitable for the coating of a fiber web layer for use in a face mask.

[0081] Any of a variety of suitable monomers may be used in a plasma. In some embodiments, a plasma comprises an organic monomer such as ethylene, butadiene acetylene, methane, methanol, or ethanol. In some embodiments, the organic monomer may be a hydrocarbon monomer (e.g., ethylene, butadiene, acetylene, or methane). In some embodiments, plasma deposition of organic monomers forms an organic polymer. In some embodiments, a plasma comprises a silicon-based monomer such as a silane (e.g., tetramethylorthosilicate, tetraethylorthosilicate, hexadecyltrimethoxysilane, or vinyltrimethylsilane) or a siloxane (e.g., hexamethyldisiloxane, hexadecyltrimethoxysilane, or hexaethyldisiloxane), or combinations thereof. A plasma may comprise exactly one type of monomer or a combination of types of monomers. In some embodiments, a plasma used for depositing nanostructures described herein does not include a silane or a siloxane.

[0082] In some embodiments, a plasma used for nanostructure deposition comprises a reactive species. For example, a plasma may comprise a reactive species such as such as oxygen, argon, helium, neon, krypton, xenon, or combination thereof. In some embodiments, a reactive species reacts with monomers of a plasma prior to deposition of the monomers onto a layer. Reaction of the monomers with the reactive species may result in the formation of radicalized monomers of the plasma. Radicalized monomers may deposit on the layers at different rates, and may impact the plasma conditions appropriate for nanostructure deposition.

[0083] A plasma suitable for depositing a nanostructure (e.g., plasma 320 of FIG. 3) described herein may be used in a chamber having any of a variety of suitable pressures. In some embodiments, a plurality of nanostructures are plasma-deposited in a chamber having a pressure of greater than or equal to 0.01 Pa, greater than or equal to 0.02 Pa, greater than or equal to 0.05 Pa, greater than or equal to 0.1 Pa, greater than or equal to 0.2 Pa, greater than or equal to 0.5 Pa, greater than or equal to 1 Pa, greater than or equal to 2 Pa, greater than or equal to 5 Pa, or greater than or equal to 10 Pa. In some embodiments, a plurality of nanostructures are plasma-deposited in a chamber having a pressure of less than or equal to 20 Pa, less than or equal to 15 Pa, less than or equal to 10 Pa, less than or equal to 5 Pa, less than or equal to 2 Pa, less than or equal to 1 Pa, less than or equal to 0.5 Pa, less than or equal to 0.2 Pa, less than or equal to 0.1 Pa, less than or equal to 0.05 Pa, or less than or equal to 0.02 Pa. Combinations of these ranges are also possible (e.g., greater than or equal to 0.01 Pa and less than or equal to 20 Pa or greater than or equal to 0.1 Pa and less than or equal to 10 Pa). Other ranges are also possible. A suitable plasma pressure may be chosen, for example, to produce nanostructures instead of a uniform layer.

[0084] Generally, the plasmas described herein are provided with power. The power is radio-frequency (RF) power or microwave (MW) power, in some embodiments. A plasma for depositing a nanostructure (e.g., plasma 320 of FIG. 3) may have any of a variety of suitable powers. In some embodiments, a plasma for depositing a nanostructure has a power of greater than or equal to 800 W, greater than or equal to 820 W, greater than or equal to 850 W, greater than or equal to 880 W, greater than or equal to 900 W, greater than or equal to 920 W, greater than or equal to 950 W, greater than or equal to 980 W, greater than or equal to 1000 W, greater than or equal to 1020 W, greater than or equal to 1050 W, greater than or equal to 1080 W, greater than or equal to 1100 W, greater than or equal to 1120 W, greater than or equal to 1150 W, greater than or equal to 1180 W, greater than or equal to 1200 W, greater than or equal to 1220 W, greater than or equal to 1250 W, or greater than or equal to 1280 W. In some embodiments, a plasma for depositing a nanostructure has a power of less than or equal to 1300 W, less than or equal to 1280 W, less than or equal to 1250 W, less than or equal to 1220 W, less than or equal to 1200 W, less than or equal to 1180 W, less than or equal to 1150 W, less than or equal to 1120 W, less than or equal to 1100 W, less than or equal to 1080 W, less than or equal to 1050 W, less than or equal to 1020 W, less than or equal to 1000 W, less than or equal to 980 W, less than or equal to 950 W, less than or equal to 920 W, less than or equal to 900 W, less than or equal to 880 W, less than or equal to 850 W, or less than or equal to 820 W. Combinations of these ranges are also possible (e.g., greater than or equal to 800 W and less than or equal to 1300 W or greater than or equal to 900 and less than or equal to 1250 W). Other ranges are also possible.

[0085] A method may comprise depositing a coating layer at a surface of a layer (e.g., a support layer that may be a first layer or a third layer) such that the surface comprises the coating layer. The coating layer may be deposited on top of a plurality of nanostructures (e.g., on top of a plurality of nanowires at a surface of a face mask or layer, such as a support layer that may be a first layer or third layer). For example, referring again to FIG. 3, a method step 352 comprises depositing a coating layer 313 on top of nanostructures 307. A coating layer formed on top of a plurality of nanostructures may retain a texture of the plurality of nanostructures. For example, as shown in FIG. 3, coating layer 313 retains a texture that includes hills 397 (e.g., the coating layer is higher above nanostructures 307) and valleys 399 (e.g., the coating layer is lower elsewhere). A coating layer having such undulations (e.g., hills and valleys, protrusions and indentations) positioned on top of a plurality of nanostructures may have increased oleophobicity and / or hydrophobicity relative to an analogous flat coating layer having an identical composition (e.g., absent the nanostructures, all other factors being equal), since the coating layer’s texture may create the same increase in contact angle described above with reference to FIG. 2B. For instance, the increase in oleophobicity and / or hydrophobicity and / or contact angle resulting from the presence of the coating layer over the nanostructures may be attributable to the presence of an ambient gas between the nanostructures.

[0086] A coating layer may be deposited at a surface of a layer (e.g., at a surface of a support layer that may be a first layer or a third layer) by any of a variety of appropriate methods. In some embodiments, a coating layer is deposited using plasma. For example, as shown in FIG. 3, coating layer 313 is deposited using a plasma 322. A plasma used to deposit a coating layer may comprise a monomer such as an organic monomer and / or a silicon-based monomer (e.g., a silane or a siloxane). Appropriate types of organic and silicon-based monomers are discussed above, in the context of plasmas used to form nanostructures — any monomer listed there may be used for coating layer formation. According to some embodiments, a method comprises polymerizing monomers from a plasma to form a coating layer at a surface of a layer (e.g., a support layer that may be a first layer or a third layer). A coating layer formed by plasma deposition may comprise a polymerized form of a monomer in the plasma (i.e., a polymer formed from plasma polymerization). Appropriate pressure and power conditions for the plasma may be used to form a uniform coating layer. In some embodiments, a surface of a face mask comprises a coating layer comprising an organic polymer, a polymerized silane and / or a polymerized siloxane. In some embodiments, a coating layer comprises exactly one polymer selected from the group consisting of an organic polymer, a polymerized silane and / or a polymerized siloxane. However, in other embodiments a coating layer may comprise two or more polymers selected from the group consisting of an organic polymer, a polymerized silane and / or a polymerized siloxane. The composition of a coating layer may be homogeneous, or may comprise a composition gradient (e.g., along the depth dimension of the coating layer), as described in more detail below.

[0087] In some embodiments, a plasma used for coating layer deposition comprises a reactive species. For example, a plasma may comprise a reactive species such as such as oxygen, argon, helium, neon, krypton, xenon, or combination thereof. In some embodiments, a reactive species may etch a coating layer as the coating layer is deposited (as discussed in greater detail below). However, in some embodiments, a reactive species reacts with monomers of a plasma prior to deposition of the monomers onto a coating layer. Reaction of the monomers with the reactive species may result in the formation of radicalized monomers of the plasma. Radicalized monomers may deposit on the coating layers at different rates, and may cause changes to properties of a deposited coating layer.

[0088] A plasma suitable for depositing a coating layer (e.g., plasma 322 of FIG. 3) described herein may be used in a chamber having any of a variety of suitable pressures. In some embodiments, a coating layer is plasma-deposited in a chamber having a pressure of greater than or equal to 5 Pa, greater than or equal to 10 Pa, greater than or equal to 15 Pa, greater than or equal to 20 Pa, greater than or equal to 25 Pa, greater than or equal to 30 Pa, greater than or equal to 35 Pa, greater than or equal to 40 Pa, greater than or equal to 45 Pa, greater than or equal to 50 Pa, greater than or equal to 55 Pa, greater than or equal to 60 Pa, greater than or equal to 65 Pa, greater than or equal to 70 Pa, greater than or equal to 75 Pa, greater than or equal to 80 Pa, or greater than or equal to 85 Pa. In some embodiments, a coating layer is plasma-deposited in a chamber having a pressure of less than or equal to 90 Pa, less than or equal to 85 Pa, less than or equal to 80 Pa, less than or equal to 75 Pa, less than or equal to 70 Pa, less than or equal to 65 Pa, less than or equal to 60 Pa, less than or equal to 55 Pa, less than or equal to 50 Pa, less than or equal to 45 Pa, less than or equal to 40 Pa, less than or equal to 35 Pa, less than or equal to 30 Pa, less than or equal to 25 Pa, less than or equal to 20 Pa, less than or equal to 15 Pa, or less than or equal to 10 Pa. Combinations of these ranges are also possible (e.g., greater than or equal to 5 Pa and less than or equal to 90 Pa, greater than or equal to 20 Pa and less than or equal to 80 Pa, greater than or equal to 40 Pa and less than or equal to 60 Pa, or greater than or equal to 10 Pa and less than or equal to 40 Pa). It should be understood that the aforementioned ranges may refer to plasmas comprising any of the types of monomers described above, and that different pressures may be suitable for deposition of different coating layers, depending on the embodiment. Other ranges are also possible.

[0089] A plasma for depositing a coating layer (e.g., plasma 322 of FIG. 3) may have any of a variety of suitable powers. In some embodiments, a plasma for depositing a coating layer has a power of greater than or equal to 500 W, greater than or equal to 550 W, greater than or equal to 600 W, greater than or equal to 650 W, greater than or equal to 700 W, greater than or equal to 750 W, greater than or equal to 800 W, greater than or equal to 850 W, greater than or equal to 900 W, greater than or equal to 950 W, greater than or equal to 1000 W, greater than or equal to 1050 W, greater than or equal to 1100 W, greater than or equal to 1150 W, greater than or equal to 1200 W, greater than or equal to 1250 W, greater than or equal to 1300 W, greater than or equal to 1350 W, greater than or equal to 1400 W, or greater than or equal to 1450 W. In some embodiments, a plasma for depositing a coating layer has a power of less than or equal to 1500 W, less than or equal to 1450 W, less than or equal to 1400 W, less than or equal to 1350 W, less than or equal to 1300 W, less than or equal to 1250 W, less than or equal to 1200 W, less than or equal to 1150 W, less than or equal to 1100 W, less than or equal to 1050 W, less than or equal to 1000 W, less than or equal to 950 W, less than or equal to 900 W, less than or equal to 850 W, less than or equal to 800 W, less than or equal to 750 W, less than or equal to 700 W, less than or equal to 650 W, less than or equal to 600 W, or less than or equal to 550 W. Combinations of these ranges are also possible (e.g., greater than or equal to 500 W and less than or equal to 1500 W, greater than or equal to 500 W and less than or equal to 1000 W, or greater than or equal to 700 W and less than or equal to 950 W). Other ranges are also possible.

[0090] A coating layer positioned on top of on top of a plurality of nanostructures at a surface of a layer (e.g., on a support layer that may be a first layer or a third layer) may have any of a variety of appropriate compositions. In some embodiments, a coating layer formed on top of a plurality of nanostructures is or comprises a polymerized silane. In some embodiments, a coating layer formed on top of a plurality of nanostructures is or comprises a polymerized siloxane. A coating layer comprising a polymerized silane and / or a polymerized siloxane (e.g., a coating layer that is a polymerized silane or a coating layer that is a polymerized siloxane) may have advantages for repelling oil and / or water from the face mask. However, it should be understood that a coating layer positioned on top of a plurality of nanostructures may comprise or be an organic polymer. The material of a coating layer positioned on top of a plurality of nanostructures may have a uniform composition, or may have a concentration gradient as discussed in greater detail below.

[0091] In some embodiments, a coating layer covers at least a portion of a plurality of nanostructures positioned at a surface of a layer (e.g., a support layer that may be a first layer or a third layer). In some embodiments, a face mask comprises a coating layer that covers greater than or equal to 1%, greater than or equal to 5%, greater than or equal to 10%, greater than or equal to 15%, greater than or equal to 25%, greater than or equal to 50%, greater than or equal to 75%, greater than or equal to 90%, greater than or equal to 95%, or greater than or equal to 99% of a plurality of nanostructures positioned on a surface of a coating layer. In some embodiments, a face mask comprises a coating layer that covers less than or equal to 100%, less than or equal to 99%, less than or equal to 95%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50% of a plurality of nanostructures positioned on a surface of a coating layer. Combinations of these ranges are also possible (e.g., greater than or equal to 1% and less than or equal to 100%, greater than or equal to 25% and less than or equal to 100%, or greater than or equal to 50% and less than or equal to 100%). Other ranges are also possible. A face mask described herein may comprise a coating layer covering a plurality of nanostructures and having any of a variety of suitable thicknesses. In some embodiments, a face mask comprises a coating layer having a thickness of greater than or equal to 4 nm, greater than or equal to 5 nm, greater than or equal to 6 nm, greater than or equal to 7 nm, greater than or equal to 8 nm, greater than or equal to 9 nm, greater than or equal to 10 nm, greater than or equal to 20 nm, greater than or equal to 30 nm, greater than or equal to 40 nm, greater than or equal to 50 nm, greater than or equal to 60 nm, greater than or equal to 70 nm, greater than or equal to 80 nm, greater than or equal to 90 nm, greater than or equal to 100 nm, greater than or equal to 120 nm, greater than or equal to 150 nm, greater than or equal to 180 nm, greater than or equal to 200 nm, greater than or equal to 220 nm, greater than or equal to 250 nm, greater than or equal to 280 nm, greater than or equal to 300 nm, greater than or equal to 500 nm, greater than or equal to 800 nm, greater than or equal to 1000 nm, greater than or equal to 1200 nm, greater than or equal to 1500 nm, greater than or equal to 1800 nm, greater than or equal to 2000 nm, greater than or equal to 3000 nm, greater than or equal to 4000 nm, or greater than or equal to 5000 nm. In some embodiments, a face mask comprises a coating layer covering a plurality of nanostructure and having a thickness of less than or equal to 10000 nm, less than or equal to 8000 nm, less than or equal to 5000 nm, less than or equal to 4000 nm, less than or equal to 3000 nm, less than or equal to 2000 nm, less than or equal to 1800 nm, less than or equal to 1500 nm, less than or equal to 1200 nm, less than or equal to 1000 nm, less than or equal to 800 nm, less than or equal to 500 nm, less than or equal to 300 nm, less than or equal to 280 nm, less than or equal to 250 nm, less than or equal to 220 nm, less than or equal to 200 nm, less than or equal to 180 nm, less than or equal to 150 nm, less than or equal to 120 nm, less than or equal to 100 nm, less than or equal to 90 nm, less than or equal to 80 nm, less than or equal to 70 nm, less than or equal to 60 nm, less than or equal to 50 nm, less than or equal to 40 nm, less than or equal to 30 nm, less than or equal to 20 nm, less than or equal to 10 nm, less than or equal to 9 nm, less than or equal to 8 nm, or less than or equal to 7 nm. Combinations of these ranges are also possible (e.g., greater than or equal to 7 nm and less than or equal to 10000 nm, greater than or equal to 20 nm and less than or equal to 50 nm, greater than or equal to 20 nm and less than or equal to 40 nm, greater than or equal to 100 nm and less than or equal to 200 nm, or greater than or equal to 30 nm and less than or equal to 50 nm). Other ranges are also possible. According to another aspect, a method of forming a face mask involving etching is provided. The method may comprise forming nanostructures by etching a coating layer formed at a surface of a layer (e.g., a support layer that may be a first layer or a third layer). FIG. 4 presents a schematic illustration of a nonlimiting method of face mask formation using such a bottom-up approach. As shown in FIG. 4, a method may comprise a first step of forming a coating layer 433 on top of a coating layer 401.

[0092] A coating layer suitable for etching may be formed by one or more methods described above. For example, coating layer 433 may be formed by exposing coating layer 401 to a plasma 420 comprising a monomer (e.g., an organic monomer) at an appropriate pressure and power to form a uniform coating layer, as described above. In some embodiments, method comprises forming a coating layer that comprises or consists of an organic polymer on top of a coating layer. Coating layer 433 may comprise a polymer. For example, coating layer 433 comprises an organic polymer polymerized from an organic monomer in plasma 420, according to some embodiments.

[0093] After the formation of a coating layer at a surface of a layer (e.g., a support layer that may be a first layer or a third layer), in some embodiments, the coating layer is etched to form an etched coating layer. An etched coating layer may comprise a plurality of nanostructures formed from the material of the coating layer. In some embodiments, etching is performed using a plasma. For example, referring again to the method of FIG. 4, a second method step 452 comprises forming an etched coating layer 437 comprising a plurality of nanostructures 435 by etching coating layer 433 using a second plasma 422.

[0094] Any of a variety of suitable plasmas may be used to etch a coating layer. In some embodiments, a plasma used for etching comprises a reactive species such as oxygen, argon, helium, neon, krypton, xenon, or combination thereof. A reactive species may, upon contacting a coating layer, etch the coating layer by reacting with a polymer of the coating layer. An etching process may result in the formation of a plurality of nanostructures by removing material between the nanostructures. An etched coating layer may have an increased oleophobicity and / or hydrophobicity relative to a similar smooth coating layer. An increased oleophobicity and / or hydrophobicity may result from the mechanism described above with reference to FIG. 2B, e.g., the presence of a gas between the nanostructures. A plasma suitable for etching a coating layer may be used in a chamber having any of a variety of suitable pressures. In some embodiments, a coating layer is plasma- etched in a chamber having a pressure of greater than or equal to 10 Pa, greater than or equal to 15 Pa, greater than or equal to 20 Pa, greater than or equal to 25 Pa, greater than or equal to 30 Pa, greater than or equal to 35 Pa, greater than or equal to 40 Pa, greater than or equal to 45 Pa, greater than or equal to 50 Pa, greater than or equal to 55 Pa, greater than or equal to 60 Pa, greater than or equal to 65 Pa, greater than or equal to 70 Pa, greater than or equal to 75 Pa, greater than or equal to 80 Pa, greater than or equal to 85 Pa, greater than or equal to 90 Pa, or greater than or equal to 95 Pa. In some embodiments, a coating layer is plasma-etched in a chamber having a pressure of less than or equal to 100 Pa, less than or equal to 95 Pa, less than or equal to 90 Pa, less than or equal to 85 Pa, less than or equal to 80 Pa, less than or equal to 75 Pa, less than or equal to 70 Pa, less than or equal to 65 Pa, less than or equal to 60 Pa, less than or equal to 55 Pa, less than or equal to 50 Pa, less than or equal to 45 Pa, less than or equal to 40 Pa, less than or equal to 35 Pa, less than or equal to 30 Pa, less than or equal to 25 Pa, less than or equal to 20 Pa, or less than or equal to 15 Pa. Combinations of these ranges are also possible (e.g., greater than or equal to 10 Pa and less than or equal to 100 Pa, greater than or equal to 20 Pa and less than or equal to 80 Pa, or greater than or equal to 40 Pa and less than or equal to 80 Pa). Other ranges are also possible.

[0095] A plasma for etching a coating layer may have any of a variety of suitable powers. In some embodiments, a coating layer is etched using a plasma having a power of greater than or equal to 400 W, greater than or equal to 450 W, greater than or equal to 500 W, greater than or equal to 550 W, greater than or equal to 600 W, greater than or equal to 650 W, greater than or equal to 700 W, greater than or equal to 750 W, greater than or equal to 800 W, greater than or equal to 850 W, greater than or equal to 900 W, greater than or equal to 950 W, greater than or equal to 1000 W, or greater than or equal to 1050 W. In some embodiments, a coating layer is etched using a plasma having a power of less than or equal to 1100 W, less than or equal to 1050 W, less than or equal to 1000 W, less than or equal to 950 W, less than or equal to 900 W, less than or equal to 850 W, less than or equal to 800 W, less than or equal to 750 W, less than or equal to 700 W, less than or equal to 650 W, less than or equal to 600 W, less than or equal to 550 W, less than or equal to 500 W, or less than or equal to 450 W. Combinations of these ranges are also possible (e.g., greater than or equal to 400 W and less than or equal to 1100 W or greater than or equal to 500 W and less than or equal to 1000 W). Other ranges are also possible.

[0096] Using a plasma to etch a uniform coating layer to form nanostructures may present a number of technical challenges on certain coating layers. For example, in some embodiments it is desirable for a plasma to etch different portions of a coating layer at different rates (e.g., in order to form nanostructures). In some embodiments, a method described herein involves heterogeneous etching of a coating layer (i.e., the formation of heterogeneous nanostructures on the coating layer). Heterogeneous etching of a coating layer may be performed using an electrode (e.g., involving a sputtering process). This technique may have advantages for the formation of nanostructures on face mask surfaces.

[0097] In some embodiments, an electrode is placed proximate a coating layer at a surface of a layer (e.g., a support layer that may be a first layer, a third layer) during etching. An electrode may be situated such that a plasma may be used to sputter material from the electrode to a surface of the layer. For example, an electrode may be situated on a side of a coating layer opposite a plasma, such that the plasma contacts both the coating layer and the electrode. In some embodiments, at least a portion of an electrode extends beyond an edge of a coating layer. An electrode may have a wider area than a coating layer, or may be situated such that the electrode is offset from the coating layer. In some embodiments, an electrode is a metal electrode. For example, an electrode may be or comprise aluminum, copper, and / or iron. In some embodiments, the electrode is aluminum, copper, or stainless steel. The electrode may have a charge that opposes a charge of a plasma used for etching, in some embodiments.

[0098] Material from an electrode may be sputtered onto a surface of layer (e.g., onto a surface of a support layer such as a first layer or a third layer) that is opposite the electrode. A sputtered material may have the form of nanoparticles (e.g., metal nanoparticles). In some embodiments, a material is sputtered from an exposed portion of an electrode (e.g., a portion of an electrode that is directly exposed to a plasma). In some embodiments, nanoparticles sputtered onto a surface of an electrode may result in the formation of nanostructures. Nanostructures may form for any of a variety of appropriate reasons. Without wishing to be bound by any particular theory, charged nanoparticles may repel an etching plasma, reducing local etching. Again without wishing to be bound by any particular theory, nanoparticles may act as nucleation sites around which nanostructures may develop. In some embodiments nanostructures form through other mechanisms, or through a variety of mechanisms acting in combination.

[0099] An electrode described herein may be separated from a coating layer by any of a variety of appropriate distances during etching. In some embodiments, during etching, an electrode and a coating layer are separated by a distance of greater than or equal to 0.005 mm, greater than or equal to 0.01 mm, greater than or equal to 0.02 mm, greater than or equal to 0.05 mm, greater than or equal to 0.08 mm, greater than or equal to 0.1 mm, greater than or equal to 0.2 mm, greater than or equal to 0.5 mm, or greater than or equal to 0.8 mm. In some embodiments, during etching, an electrode and a coating layer are separated by a distance of less than or equal to 1 mm, less than or equal to 0.8 mm, less than or equal to 0.5 mm, less than or equal to 0.2 mm, less than or equal to 0.1 mm, less than or equal to 0.08 mm, less than or equal to 0.05 mm, less than or equal to 0.02 mm, less than or equal to 0.01 mm, less than or equal to 0.008 mm, less than or equal to 0.005 mm, or less than or equal to 0.002 mm. Combinations of these ranges are also possible (e.g., greater than or equal to 0.001 mm and less than or equal to 1 mm). Other ranges are also possible.

[0100] In some embodiments a method comprises depositing a second coating layer at a surface of a layer (e.g., a support layer that may be a first layer or a third layer), such that the surface comprises a second coating layer that is at least partially positioned on an etched coating layer. Referring again to FIG. 4, a non-limiting method step 454 comprises depositing a second coating layer 413 on top of first, etched coating layer 437. A second coating layer may be deposited by any of a variety of methods, including any of the methods described herein. For example, as shown in FIG. 4, second coating layer 413 may be deposited using a plasma 424 analogous to plasma 322 used to deposit coating layer 313 as illustrated in FIG. 3. A second coating layer may have any of a variety of suitable compositions and properties, including any of the compositions and properties described herein. For example, in some embodiments, a second coating layer is or comprises a polymerized silane or a polymerized siloxane.

[0101] A second coating layer may cover any of a variety of suitable portions of an etched coating layer. In some embodiments, a face mask comprises a coating layer that covers greater than or equal to 1%, greater than or equal to 5%, greater than or equal to 10%, greater than or equal to 15%, greater than or equal to 25%, greater than or equal to 50%, greater than or equal to 75%, greater than or equal to 90%, greater than or equal to 95%, or greater than or equal to 99% of the area of an etched coating layer. In some embodiments, a face mask comprises a coating layer that covers less than or equal to 100%, less than or equal to 99%, less than or equal to 95%, less than or equal to 90%, less than or equal to 75%, or less than or equal to 50% of the area of an etched coating layer. Combinations of these ranges are also possible (e.g., greater than or equal to 1% and less than or equal to 100%, greater than or equal to 25% and less than or equal to 100%, or greater than or equal to 50% and less than or equal to 100%). Other ranges are also possible.

[0102] In yet another aspect, a method of forming a face mask comprising a gradient is provided. The gradient may include, for example, a mixture of two different types of polymers. In some embodiments, a method of forming a face mask comprises forming a coating layer at a surface of a layer (e.g., a support layer that may be a first layer, a third layer), wherein the coating layer comprises at least two components selected from the group of: a polymerized silane, a polymerized siloxane, and a polymer (e.g., an organic polymer). A coating layer comprising a composition gradient between at least two components selected from the group of: a polymerized silane, a polymerized siloxane, and a polymer may be formed by plasma deposition. Without wishing to be bound by any particular theory, in some embodiments, a coating layer may be deposited using a multicomponent plasma. For example, a coating layer may be deposited using a plasma comprising at least two components selected from the group of a siloxane, a silane, and a monomer that is not a silane or siloxane (e.g., an organic monomer). It is advantageous, according to some embodiments, to include an organic polymer in a coating layer comprising a concentration gradient.

[0103] Without wishing to bound by any particular theory, in some embodiments a composition gradient within a coating layer may be created by controlling a relative amount of each monomer of the plasma. In some embodiments, a ratio between a relative amount of each plasma component is varied continuously, producing a continuous concentration gradient in a coating layer. In some embodiments, a ratio between a relative amount of each plasma component is varied discontinuously, in a plurality of steps, but a continuous concentration gradient still arises. Without wishing to be bound by any particular theory, a continuous concentration gradient may arise from discontinuous changes in plasma composition as a result of surface effects, monomer diffusion within a coating layer, or by any of a variety of other mechanisms.

[0104] A coating layer comprising a composition gradient may be produced using any of a variety of appropriate plasmas. In some embodiments, a composition gradient is produced using a plasma comprising: at least one organic monomer selected from the group consisting of: ethylene, butadiene acetylene, methane, methanol, and ethanol; and at least one silane selected from the group consisting of tetramethylorthosilicate, tetraethylorthosilicate, hexadecyltrimethoxysilane, and vinyltrimethylsilane. According to some embodiments, a composition gradient is produced using a plasma comprising: at least one organic monomer selected from the group consisting of: ethylene, butadiene acetylene, methane, methanol, and ethanol; and at least one siloxane selected from the group consisting of hexadecyltrimethoxysilane, and hexaethyldisiloxane. In some embodiments, a composition gradient is produced using a plasma comprising: at least one organic monomer selected from the group consisting of ethylene, butadiene acetylene, methane, methanol, and ethanol: at least one silane selected from the group consisting of tetramethylorthosilicate, tetraethylorthosilicate, hexadecyltrimethoxysilane, and vinyltrimethylsilane; and at least one siloxane selected from the group consisting of hexadecyltrimethoxysilane, and hexaethyldisiloxane. It should, of course, be understood that concentration gradient may be produced using plasmas comprising more than two monomers, and / or comprising monomers not listed above.

[0105] A plasma used to deposit a coating layer comprising a composition gradient may have any of a variety of appropriate powers and pressures, including the powers and pressures described in the context of coating layer deposition, above. In some embodiments, plasmas with pressures of greater than or equal to 20 Pa and less than or equal to 60 Pa have been found to be advantageous for depositing coating layers with composition gradients. In some embodiments, plasmas with powers of greater than or equal to 700 W and less than or equal to 1000 W have been found to be advantageous for depositing coating layers with composition gradients.

[0106] A first coating layer comprising a composition gradient and a second coating layer comprising a composition gradient may each independently be formed on a coating layer by a method of coating layer formation described above. In some embodiments, a first coating layer is between a second coating layer and a coating layer.

[0107] In the context of the present disclosure, it has been recognized that face masks comprising multiple coating layers with composition gradients may have favorable elastic, water repellent, and / or oil repellent properties. Without wishing to be bound by any particular theory, composition gradients of coating layers on a coating layer may preserve desirable surface properties (e.g., high hydrophobicity and / or oleophobicity) while preserving mechanical compatibility between the coating layers and the coating layer. A first coating layer and a second coating layer may have the same or different compositions. A first coating layer and a second coating layer may have a same or different composition gradients. In some embodiments, it may be advantageous for one or more coating layers on a coating layer to have a polymerize silane and / or or a polymerized siloxane concentration that increases with distance away from the coating layer (e.g., across a thickness of the coating layer(s)). In some embodiments, it may be advantageous for one or more coating layers on a coating layer to have an organic polymer concentration that decreases with distance away from the coating layer (e.g., across a thickness of the coating layer(s)).

[0108] A coating layer comprising a composition gradient may be etched, but the disclosure is not limited to coating layers that have been etched. Similarly, a coating layer comprising a composition gradient may be deposited on top of a plurality of nanostructures, but the disclosure is not limited to coating layers that have been deposited on a plurality of nanostructures.

[0109] A face mask formed as described herein may repel oil and / or water. Without wishing to be bound by any particular theory, the ability of a face mask to repel oil and / or water may be related to a surface energy of a surface of the face mask. However, the present disclosure recognizes that, according to some embodiments, surface features (e.g., nanostructures or coating layers deposited thereon) may advantageously improve the ability of a coating layer to repel oil and / or water. Such improvements in oil and / or water repellency may result from trapping of air between nanostructures, which may reduce the ability of liquids like oil and water to wet a surface of a face mask, however other mechanisms are also possible. Oil and / or water repellency may be desirable for a number of applications, particularly in the context of face masks. In some embodiments, a surface of a face mask described herein is hydrophobic. Generally, water contacting a hydrophobic surface of a face mask has a contact angle. A face mask described herein may have any of a variety of suitable contact angles with water. In some embodiments, a hydrophobic surface of a face mask has a water contact angle of greater than or equal to 90°, greater than or equal to 95°, greater than or equal to 100°, greater than or equal to 105°, greater than or equal to 110°, greater than or equal to

[0110] 115°, greater than or equal to 120°, greater than or equal to 125°, greater than or equal to

[0111] 130°, greater than or equal to 135°, greater than or equal to 140°, greater than or equal to

[0112] 145°, greater than or equal to 150°, greater than or equal to 155°, greater than or equal to

[0113] 160°, greater than or equal to 165°, greater than or equal to 170°, greater than or equal to

[0114] 175°, or greater. In some embodiments, a hydrophobic surface of a face mask has a water contact angle of less than or equal to 180°, less than or equal to 175°, less than or equal to 170°, less than or equal to 165°, less than or equal to 160°, less than or equal to 155°, less than or equal to 150°, less than or equal to 145°, less than or equal to 130°, less than or equal to 125°, less than or equal to 120°, less than or equal to 115°, less than or equal to 110°, less than or equal to 105°, less than or equal to 100°, or less than or equal to 95°. Combinations of these ranges are also possible (e.g., greater than or equal to 90° and less than or equal to 180°, greater than or equal to 120° and less than or equal to 180°, or greater than or equal to 140° and less than or equal to 180°). Other ranges are also possible.

[0115] The contact angle may be measured by the sessile drop technique.

[0116] According to some embodiments some embodiments, hydrophobicity of a surface of a face mask is characterized by its hydrophobicity rank. In some embodiments, a surface of a face mask has a hydrophobicity rank of greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, or greater than or equal to 7. In some embodiments, a surface of a face mask has a hydrophobicity rank of less than or equal to 8, less than or equal to 7, less than or equal to 6, less than or equal to 5, less than or equal to 4, less than or equal to 3, or less than or equal to 2. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal to 1 and less than or equal to 8, greater than or equal to 1 and less than or equal to 5, or greater than or equal to 1 and less than or equal to 3). Other ranges are also possible. In some embodiments, a surface of a face mask is not hydrophobic and has a hydrophobicity rank of 0.

[0117] Hydrophobicity rank as described herein is determined according to AATCC TM 193-2017 measured after conditioning for 4 hours at 21+2 °C and 65+5% relative humidity (RH). Briefly, a set of 8 test solutions comprising different volumetric ratios of water and isopropanol are used. 3 drops of each test solution (having an average volume of about 0.05 mL) are dropped on a surface of a face mask from a height of about 0.6 cm above the surface of the face mask. The test solution having the highest proportion of isopropanol that does not wet the surface of the face mask (by forming a contact angle of less than or equal to 75° with the surface of the face mask) within 10 seconds corresponds to the hydrophobicity rank. For example, if a test solution with a 60:40 water: isopropyl alcohol (vol: vol) with a surface tension of 25.4 mN / m does not wet the surface of the face mask within 10 seconds, but a test solution with a 50:50 water:isopropyl alcohol (vokvol) with a surface tension of 24.5 mN / m wets the surface of the face mask within 10 seconds, then the surface of the face mask has a hydrophobicity rank of 6.

[0118] A face mask may have a surface that is oleophobic. Generally, an oleophobic surface of a face mask comprises at least one oleophobic surface. The oleophobicity of the surface of the face mask may be characterized by an oleophobicity rank of the surface of the face mask. A surface of a face mask described herein may have any of a variety of suitable oleophobicity ranks. In some embodiments, a surface of a face mask has an oleophobicity rank of greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 4.5, greater than or equal to 5, greater than or equal to 5.5, greater than or equal to 6, greater than or equal to 6.5, greater than or equal to 7, or greater than or equal to 7.5. In some embodiments, a surface of a face mask has an oleophobicity rank of less than or equal to 8, less than or equal to 7.5, less than or equal to 7, less than or equal to 6.5, less than or equal to 6, less than or equal to 5.5, less than or equal to 5, less than or equal to 4.5, less than or equal to 4, less than or equal to 3, or less than or equal to 2. Combinations of the abovereferenced ranges are also possible (e.g., greater than or equal to 1 and less than or equal to 8, greater than or equal to 1 and less than or equal to 5, or greater than or equal to 1 and less than or equal to 3). Other ranges are also possible. In some embodiments, a surface of a face mask described herein is not oleophobic and has an oleophobicity rank of O.

[0119] Oleophobicity rank as described herein is determined according to AATCC TM 118-2017 measured at after conditioning for 4 hours at 21+2 °C and 65+5% relative humidity (RH). Briefly, 5 drops of each test oil (having an average droplet diameter of about 2 mm) are placed on five different locations on the surface of the face mask. The test oil with the greatest oil surface tension that does not wet a surface of the face mask (e.g., has a contact angle greater than or equal to 90 degrees with the surface of the face mask) after 30 seconds of contact with the surface of the face mask corresponds to the oleophobicity rank. For example, if a test oil with a surface tension of 26.6 mN / m does not wet the surface of the face mask after 30 seconds, but a test oil with a surface tension of 25.4 mN / m wets the surface of face mask within thirty seconds, the surface of the face mask has an oleophobicity rank of 4. In some embodiments, if three of more of the five drops partially wet the surface (e.g., by forming a droplet, but not a well-rounded drop on the surface) in a given test, then the oleophobicity rank is expressed to the nearest 0.5 value determined by subtracting 0.5 from the number of the test liquid. By way of example, if a test oil with a surface tension of 25.4 mN / m does not wet the surface of a face mask after 30 seconds, but a test oil with a surface tension of 23.8 mN / m only partially wets the surface of the face mask after 30 seconds (e.g., three or more of the test droplets form droplets on the surface of the surface of the face mask that are not well- rounded droplets) within thirty seconds, the surface of the face mask has an oleophobicity rank of 5.5.

[0120] In some embodiments, the hydrophobicity ranks and / or the oleophobicity ranks described above refer to the hydrophobicity rank and / or the oleophobicity rank of an unwashed face mask. In some embodiments, oleophobic and / or hydrophobic face masks that are capable of remaining oleophobic and / or hydrophobic after washing are desirable. For example, and face mask comprising a fiber web layer may be particularly useful if able to retain oleophobic and / or hydrophobic properties after washing.

[0121] A face mask described herein may have an oleophobicity rank and / or a hydrophobicity rank described above after being subjected to any of a variety of suitable numbers of standard wash cycles. For example, in some embodiments a face mask has an oleophobicity rank and / or a hydrophobicity rank described above after being subjected to a number of standard wash cycles greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, greater than or equal to 9, greater than or equal to 10, greater than or equal to 11, greater than or equal to 12, greater than or equal to 13, greater than or equal to 14, or greater than or equal to 15. In some embodiments a face mask has an oleophobicity rank and / or a hydrophobicity rank described above after being subjected to a number of standard wash cycles less than or equal to 20, less than or equal to 19, less than or equal to 18, less than or equal to 17, less than or equal to 16, less than or equal to 15, less than or equal to 14, less than or equal to 13, less than or equal to 12, less than or equal to 11, less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, or less than or equal to 5. In some embodiments, a face mask has an oleophobicity rank and / or a hydrophobicity rank described above after being subjected to 0 standard wash cycles. Combinations of these ranges are also possible (e.g., greater than or equal to 1 and less than or equal to 20, greater than or equal to 5 and less than or equal to 15, or greater than or equal to 10 and less than or equal to 15). These ranges may further be combined with any of the forgoing ranges (e.g., a face mask may have a hydrophobicity rank of greater than or equal to 2 and less than or equal to 4 after being subjected to a number of wash cycles greater than or equal to 10 and less than or equal to 15, a face mask may have an oleophobicity rank of greater than or equal to 1 and less than or equal to 3 after being subjected to a number of wash cycles greater than or equal to 10 and less than or equal to 15). Other ranges are also possible. Standard wash cycles may be carried out using the ISO 6003:2012(E) standard protocol.

[0122] Commercially, fluorinated polymers are often used to produce oleophobic and / or hydrophobic coating layers. However, the use of fluorinated polymers is not environmentally friendly. One advantage of the methods and face masks described herein is that they may provide oleophobic and / or hydrophobic surfaces using nanostructures and / or coating layers without fluorine, or with only trace amounts of fluorine.

[0123] In some embodiments, a face mask described herein comprises a plurality of nanostructures that comprises less than or equal to 0.5 at%, less than or equal to 0.4 at%, less than or equal to 0.3 at%, less than or equal to 0.2 at%, less than or equal to 0.1 at%, less than or equal to 0.08 at%, less than or equal to 0.05 at%, less than or equal to 0.02 at%, less than or equal to 0.01 at%, less than or equal to 0.008 at%, less than or equal to 0.005 at%, or less than or equal to 0.002 at% fluorine atoms. In some embodiments, a face mask described herein comprises a plurality of nanostructures that comprises greater than or equal to 0 at%, or greater than or equal to 0.001 at% fluorine atoms.

[0124] Combinations of these ranges are also possible (e.g., greater than or equal to 0 at% and less than or equal to 0.5 at% or greater than or equal to 0 at% and less than or equal to 0.1 at%). Other ranges are also possible.

[0125] In some embodiments, a face mask described herein comprises a coating layer that comprises less than or equal to 0.5 at%, less than or equal to 0.4 at%, less than or equal to 0.3 at%, less than or equal to 0.2 at%, less than or equal to 0.1 at%, less than or equal to 0.08 at%, less than or equal to 0.05 at%, less than or equal to 0.02 at%, less than or equal to 0.01 at%, less than or equal to 0.008 at%, less than or equal to 0.005 at%, or less than or equal to 0.002 at% fluorine atoms. In some embodiments, a face mask described herein comprises a coating layer that comprises greater than or equal to 0 at%, or greater than or equal to 0.001 at% fluorine atoms. Combinations of these ranges are also possible (e.g., greater than or equal to 0 at% and less than or equal to 0.5 at% or greater than or equal to 0 at% and less than or equal to 0.1 at%). Other ranges are also possible.

[0126] In some embodiments, the entire face mask has an amount of fluorine atoms in one or more of the above-referenced ranges.

[0127] In face masks with one or more coating layers positioned on a surface of a support layer (e.g., a support layer that may be a first layer, a third layer), the present disclosure recognizes that it may be advantageous to preserve certain relationships between mechanical properties of the coating layer(s) and mechanical properties of the support layer (e.g., the support layer that may be the first layer, the third layer). For example, when a coating layer of a face mask has elastic properties relatively similar to elastic properties of a support layer (e.g., a support layer that may be a first layer, a third layer) of the face mask upon which the coating layer is positioned, the coating layer may provide longer-lasting oleophobicity and / or hydrophobicity, improved wear resistance, or improved wash resistance. Controlling the mechanical properties of a coating layer while preserving desirable oleophobicity and / or hydrophobicity of the coating layer may present certain challenges, particularly where oleophobicity and / or hydrophobicity result exclusively from the composition of the coating layer. However, the present disclosure recognizes that the use of nanostructures and / or composition gradients within coating layers may allow control of the elastic properties of coating layers while retaining oleophobicity and / or hydrophobicity of the face mask.

[0128] A face mask herein may comprise a coating layer (e.g., a plasma-deposited coating layer) having any suitable elastic moduli. In some embodiments, a face mask comprises a coating layer (e.g., a plasma-deposited coating layer) with an elastic modulus of greater than or equal to 0.05 GPa, greater than or equal to 0.1 GPa, greater than or equal to 0.2 GPa, greater than or equal to 0.3 GPa, greater than or equal to 0.4 GPa, greater than or equal to 0.5 GPa, greater than or equal to 0.6 GPa, greater than or equal to 0.7 GPa, greater than or equal to 0.8 GPa, greater than or equal to 0.9 GPa, greater than or equal to 1 GPa, greater than or equal to 2 GPa, greater than or equal to 3 GPa, greater than or equal to 4 GPa, greater than or equal to 5 GPa, greater than or equal to 6 GPa, greater than or equal to 7 GPa, greater than or equal to 8 GPa, greater than or equal to 9 GPa, greater than or equal to 10 GPa, greater than or equal to 11 GPa, greater than or equal to 12 GPa, greater than or equal to 13 GPa, or greater than or equal to 14 GPa. In some embodiments, a face mask comprises a coating layer with an elastic modulus of less than or equal to 15 GPa, less than or equal to 14 GPa, less than or equal to 13 GPa, less than or equal to 12 GPa, less than or equal to 11 GPa, less than or equal to 10 GPa, less than or equal to 9 GPa, less than or equal to 8 GPa, less than or equal to 7 GPa, less than or equal to 6 GPa, less than or equal to 5 GPa, less than or equal to 4 GPa, less than or equal to 3 GPa, less than or equal to 2 GPa, less than or equal to 1 GPa, less than or equal to 0.9 GPa, less than or equal to 0.8 GPa, less than or equal to 0.7 GPa, less than or equal to 0.6 GPa, less than or equal to 0.5 GPa, less than or equal to 0.4 GPa, less than or equal to 0.3 GPa, less than or equal to 0.2 GPa, less than or equal to 0.1 GPa, or less than or equal to 0.05 GPa. Combinations of these ranges are also possible (e.g., greater than or equal to 0.05 GPa and less than or equal to 15 GPa, greater than or equal to 0.1 GPa and less than or equal to 0.05 GPa, greater than or equal to 1 GPa and less than or equal to 5 GPa, greater than or equal to 4 GPa and less than or equal to 12 GPa, greater than or equal to 0.5 GPa and less than or equal to 2 GPa, greater than or equal to 0.3 GPa and less than or equal to 0.8 GPa, greater than or equal to 0.1 GPa and less than or equal to 0.6 GPa, or greater than or equal to 0.5 GPa and less than or equal to 2 GPa). Other ranges are also possible. It should be understood that a face mask may comprise more than one coating layer having a modulus within a range described above.

[0129] In some embodiments, a face mask comprises a coating layer (e.g., a plasma- deposited coating layer) and a coating layer, wherein the ratio of the elastic modulus of the coating layer to the elastic modulus of the coating layer is greater than or equal to IxlO3, greater than or equal to 2xl03, greater than or equal to 5x103, greater than or equal to 8xl03, greater than or equal to IxlO4, greater than or equal to 2xl03, greater than or equal to 5xl03, greater than or equal to 8xl03, greater than or equal to IxlO4, greater than or equal to 2xl04, greater than or equal to 5xl04, greater than or equal to 8xl04, greater than or equal to IxlO5, greater than or equal to 2xl05, greater than or equal to 5xl05, greater than or equal to 8xl05, or greater than or equal to IxlO6. In some embodiments, a face mask comprises a coating layer (e.g., a plasma-deposited coating layer) and a coating layer, wherein the ratio of the elastic modulus of the coating layer to the elastic modulus of the coating layer is less than or equal to 2xl06, less than or equal to IxlO6, less than or equal to 8xl05, less than or equal to 5xl05, less than or equal to 2xl05, less than or equal to IxlO5, less than or equal to 8xl04, less than or equal to 5xl04, less than or equal to 2xl04, less than or equal to IxlO4, less than or equal to 8xl03, less than or equal to 5xl03, or less than or equal to 2xl03. Combinations of these ranges are also possible (e.g., greater than or equal to IxlO3and less than or equal to IxlO6, greater than or equal to IxlO3and less than or equal to 5xl05, or greater than or equal to IxlO4and less than or equal to IxlO6). Other ranges are also possible. In some embodiments, a face mask comprises a coating layer having a first elastic modulus, a first coating layer having a second elastic modulus, and a second coating layer having a third elastic modulus, wherein a ratio of the second elastic modulus to the first elastic modulus and a ratio of the third elastic modulus to the first elastic modulus each independently fall within one of these ranges described herein.

[0130] A face mask described herein may comprise a plurality of nanostructures. The nanostructures may be formed by any of a variety of suitable methods, including those described herein. In some embodiments, the plurality of nanostructures is discrete. For example, a first nanostructure of a plurality of nanostructures may have no direct contact with a second nanostructure of the plurality of nanostructures. Discrete nanostructures may be formed by plasma deposition of the nanostructures, as described in greater detail above. However, in some embodiments, the plurality of nanostructures is not discrete. For example, the nanostructures of the plurality may be in direct contact with one another (e.g., at bases of the nanostructures). Nanostructures in direct contact with one another may be formed, according to some embodiments, by etching a coating layer to form a plurality of nanostructures, such that nanostructures are separated from one another by an etched groove and are physically joined at a base of the groove.

[0131] The nanostructures may have any of a variety of suitable geometries. For example, in some embodiments, a nanostructure is relatively round and has a relatively uniform diameter. However, the nanostructures may be elongated or have other geometries, and the disclosure is not so limited.

[0132] In some embodiments, the nanostructures increase the roughness of a face mask. A face mask described herein may comprise a surface having any of a variety of suitable root mean squared (RMS) roughness values. In some embodiments, a face mask described herein comprises a surface having a roughness of greater than or equal to 0.05 microns, greater than or equal to 0.1 microns, greater than or equal to 0.2 microns, greater than or equal to 0.3 microns, greater than or equal to 0.4 microns, greater than or equal to 0.5 microns, greater than or equal to 0.6 microns, greater than or equal to 0.7 microns, greater than or equal to 0.8 microns, greater than or equal to 0.9 microns, greater than or equal to 0.10 microns, greater than or equal to 0.11 microns, or greater than or equal to 0.12 microns, greater than or equal to 0.13 microns, greater than or equal to 0.14 microns, greater than or equal to 0.15 microns, or greater than or equal to 0.2 microns. In some embodiments, a face mask described herein comprises a surface having a roughness of less than or equal to 0.2 microns, less than or equal to 0.15 microns, less than or equal to 0.14 microns, less than or equal to 0.13 microns, less than or equal to 0.12 microns, less than or equal to 0.11 microns, less than or equal to 0.10 microns, less than or equal to 0.9 microns, less than or equal to 0.8 microns, less than or equal to 0.7 microns, less than or equal to 0.6 microns, less than or equal to 0.5 microns, less than or equal to 0.4 microns, less than or equal to 0.3 microns, less than or equal to 0.2 microns, or less than or equal to 0.1 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.05 microns and less than or equal to 0.2 microns). Other ranges are also possible. The RMS roughness of a face mask may be determined by atomic force microscopy.

[0133] A face mask described herein may comprise nanostructures having any of a variety of suitable diameters. In some embodiments, a face mask comprises a plurality of nanostructures having an average diameter of greater than or equal to 0.05 microns, greater than or equal to 0.08 microns, greater than or equal to 0.1 microns, greater than or equal to 0.12 microns, greater than or equal to 0.15 microns, greater than or equal to 0.18 microns, greater than or equal to 0.2 microns, greater than or equal to 0.05 microns, greater than or equal to 0.22 microns, greater than or equal to 0.25 microns, greater than or equal to 0.28 microns, greater than or equal to 0.3 microns, greater than or equal to 0.32 microns, greater than or equal to 0.35 microns, greater than or equal to 0.38 microns, greater than or equal to 0.4 microns, or greater than or equal to 0.42 microns. In some embodiments, a face mask comprises a plurality of nanostructures having an average diameter of less than or equal to 0.45 microns, less than or equal to 0.42 microns, less than or equal to 0.4 microns, less than or equal to 0.38 microns, less than or equal to 0.35 microns, less than or equal to 0.32 microns, less than or equal to 0.3 microns, less than or equal to 0.28 microns, less than or equal to 0.25 microns, less than or equal to 0.22 microns, less than or equal to 0.2 microns, less than or equal to 0.18 microns, less than or equal to 0.15 microns, less than or equal to 0.12 microns, or less than or equal to 0.1 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.05 microns and less than or equal to 0.45 microns, greater than or equal to 0.1 and less than or equal to 0.4 microns, or greater than or equal to 0.12 and less than or equal to 0.38). Other ranges are also possible. The nanostructure diameter may be determined by atomic force microscopy.

[0134] In some embodiments, a face mask comprises a plurality of nanostructures having an standard deviation in diameter of greater than or equal to 0.005 microns, greater than or equal to 0.008 microns, greater than or equal to 0.01 microns, greater than or equal to 0.012 microns, greater than or equal to 0.015 microns, greater than or equal to 0.018 microns, greater than or equal to 0.02 microns, greater than or equal to 0.022 microns, greater than or equal to 0.025 microns, greater than or equal to 0.028 microns, greater than or equal to 0.03 microns, or greater than or equal to 0.032 microns. In some embodiments, a face mask comprises a plurality of nanostructures having an standard deviation in diameter of less than or equal to 0.035 microns, less than or equal to 0.032 microns, less than or equal to 0.03 microns, less than or equal to 0.028 microns, less than or equal to 0.025 microns, less than or equal to 0.022 microns, less than or equal to 0.02 microns, less than or equal to 0.018 microns, less than or equal to 0.015 microns, less than or equal to 0.012 microns, less than or equal to 0.01 microns, or less than or equal to 0.008 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.005 microns and less than or equal to 0.035 microns, greater than or equal to 0.008 microns and less than or equal to 0.030 microns, or greater than or equal to 0.008 microns and less than or equal to 0.025 microns). Other ranges are also possible. The standard deviation in nanostructure diameter may be determined by atomic force microscopy.

[0135] A face mask described herein may comprise nanostructures having any of a variety of suitable aspect ratios of nanostructure height to nanostructure diameter. In some embodiments, a face mask comprises a plurality of nanostructures having an average aspect ratio of greater than or equal to 0.5, greater than or equal to 0.6, greater than or equal to 0.7, greater than or equal to 0.8, greater than or equal to 0.9, greater than or equal to 1, greater than or equal to 2, greater than or equal to 3, greater than or equal to 4, greater than or equal to 5, greater than or equal to 6, greater than or equal to 7, greater than or equal to 8, greater than or equal to 9, greater than or equal to 10, greater than or equal to 11, or greater than or equal to 12. In some embodiments, a face mask comprises an average aspect ratio of less than or equal to 13, less than or equal to 12, less than or equal to 11, less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, less than or equal to 5, less than or equal to 4, less than or equal to 3, less than or equal to 2, less than or equal to 1, less than or equal to 0.9, less than or equal to 0.8, less than or equal to 0.7, or less than or equal to 0.6. Combinations of these ranges are also possible (e.g., greater than or equal to 0.5 and less than or equal to 13 or greater than or equal to 1 and less than or equal to 12). Other ranges are also possible. The aspect ratio of the nanostructures may be determined by atomic force microscopy.

[0136] A plurality of nanostructures may be disposed in any of a variety of suitable arrangements. For example, the nanostructures may be arranged in an ordered grid. In some embodiments, the nanostructures have a random arrangement. A random arrangement of nanostructures may be uniformly random, or may simply have a stochastic spatial distribution with high local concentrations of nanostructures in some areas and low local concentrations of nanostructures in others. One advantage of random arrangements of nanostructures may be scalability. For example, in some embodiments it is easier to fabricate random arrangements of nanostructures over large coating layer areas. Thus, random arrangements of nanostructures may have particular advantages for the use of nanostructures in face mask surfaces.

[0137] A face mask described herein may comprise nanostructures having any of a variety of suitable peak to peak spacings. In some embodiments, a face mask comprises a plurality of nanostructures having an average peak-to-peak spacing of greater than or equal to 0.2 microns, greater than or equal to 0.5 microns, greater than or equal to 0.8 microns, greater than or equal to 1 micron, greater than or equal to 1.2 microns, greater than or equal to 1.5 microns, greater than or equal to 1.8 microns, greater than or equal to 2 microns, or greater than or equal to 2.2 microns. In some embodiments, a face mask comprises a plurality of nanostructures having an average peak-to-peak spacing of less than or equal to 2.5 microns, less than or equal to 2.2 microns, less than or equal to 2 microns, less than or equal to 1.8 microns, less than or equal to 1.5 microns, less than or equal to 1.2 microns, less than or equal to 1 micron, less than or equal to 0.8 microns, less than or equal to 0.5 microns, or less than or equal to 0.2 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.2 microns and less than or equal to 2.5 microns or greater than or equal to 0.2 microns and less than or equal to 2.2 microns). Other ranges are also possible.

[0138] In some embodiments, a face mask comprises a plurality of nanostructures having a standard deviation in peak-to-peak spacing of greater than or equal to 0.001 microns, greater than or equal to 0.002 microns, greater than or equal to 0.005 microns, greater than or equal to 0.01 microns, greater than or equal to 0.02 microns, greater than or equal to 0.05 microns, greater than or equal to 0.08 microns, greater than or equal to 0.1 microns, greater than or equal to 0.2 microns, greater than or equal to 0.3 microns, or greater than or equal to 0.4 microns. In some embodiments, a face mask comprises a plurality of nanostructures having a standard deviation in peak-to-peak spacing of less than or equal to 0.5 microns, less than or equal to 0.4 microns, less than or equal to 0.3 microns, less than or equal to 0.2 microns, less than or equal to 0.1 microns, less than or equal to 0.08 microns, less than or equal to 0.05 microns, less than or equal to 0.02 microns, less than or equal to 0.01 microns, less than or equal to 0.008 microns, less than or equal to 0.005 microns, or less than or equal to 0.002 microns. Combinations of these ranges are also possible (e.g., greater than or equal to 0.001 microns and less than or equal to 0.5 microns). Other ranges are also possible.

[0139] In some embodiments, face masks comprising hydrophilic surfaces, and associated methods, are described. Like the hydrophobic surfaces described above, a hydrophilic surface of a layer may be produced using a plasma. As described above, the plasma may be used to deposit a polymeric coating layer at a surface of a layer (e.g., a support layer that may be a first layer or a third layer). The plasma may comprise a monomer, as described above. For example, in some embodiments, a plasma used to make a hydrophilic coating layer comprises an organic monomer such as ethylene, butadiene acetylene, methane, methanol, or ethanol. In some embodiments, the organic monomer may be a hydrocarbon monomer (e.g., ethylene, butadiene, acetylene, or methane).

[0140] A plasma used for hydrophilic coating layer deposition may comprise a precursor for forming a hydrophilic moiety. For example, a plasma may comprise a hydrophilic moiety precursor such as such as ammonia. The hydrophilic moiety precursor may react with the monomer, or with the deposited coating, to form hydrophilic, nitrogen-rich or hydrogen rich species. For example, ammonia may react with a monomer to form alkylamines.

[0141] Additionally, the plasma may comprise one or more, oxygen, argon, or a combination thereof. In some embodiments, a hydrophilic moiety precursor reacts with monomers of a plasma prior to deposition of the monomers onto a layer. Reaction of the monomers with the reactive species may result in the formation of radicalized monomers of the plasma.

[0142] Other plasma components described above may be used during the formation of the hydrophilic coating layer. For example, in some embodiments, a plasma used to deposit a hydrophilic coating layer comprises a reactive species. For example, a plasma may comprise a reactive species such as such as oxygen, argon, helium, neon, krypton, xenon, or combination thereof. In some embodiments, a reactive species reacts with monomers of a plasma prior to deposition of the monomers onto a layer. Reaction of the monomers with the reactive species may result in the formation of radicalized monomers of the plasma. Radicalized monomers may deposit on the layers at different rates, and may impact the plasma conditions appropriate for coating layer deposition.

[0143] The hydrophilicity of a surface of a face mask may be determined by its water contact angle (discussed above, in the context of hydrophobic water contact angles), according to some embodiments. A face mask described herein may have any of a variety of suitable contact angles with water. In some embodiments, a hydrophilic surface of a face mask has a water contact angle of greater than or equal to 0°, greater than or equal to 2°, greater than or equal to 5°, greater than or equal to 8°, greater than or equal to 10°, greater than or equal to 12°, greater than or equal to 15°, greater than or equal to 18°, greater than or equal to 20°, greater than or equal to 22°, greater than or equal to 25°, or greater than or equal to 28°, or greater. In some embodiments, a hydrophilic surface of a face mask has a water contact angle of less than or equal to 30°, less than or equal to 28°, less than or equal to 25°, less than or equal to 22°, less than or equal to 20°, less than or equal to 18°, less than or equal to 15°, less than or equal to 12°, less than or equal to 10°, less than or equal to 8°, less than or equal to 5°, less than or equal to 2°, or less. Combinations of these ranges are also possible (e.g., greater than or equal to 0° and less than or equal to 30°, greater than or equal to 0° and less than or equal to 10°, or greater than or equal to 0° and less than or equal to 5°). Other ranges are also possible.

[0144] As discussed above, the contact angle may be measured by the sessile drop technique.

[0145] A plasma used for hydrophilic coating layer deposition may comprise its constituents at any of a variety of appropriate flow rates. A plasma described herein may comprise ethylene having any of a variety of suitable flow rates. In some embodiments, a plasma comprises ethylene having a flow rate of greater than or equal to 4 seem, greater than or equal to 5 seem, greater than or equal to 6 seem, greater than or equal to 7 seem, greater than or equal to 8 seem, greater than or equal to 9 seem, greater than or equal to 10 seem, greater than or equal to 12 seem, greater than or equal to 14 seem, greater than or equal to 16 seem, greater than or equal to 18 seem, greater than or equal to 20 seem, greater than or equal to 22 seem, greater than or equal to 24 seem, greater than or equal to 26 seem, greater than or equal to 28 seem, or greater than or equal to 30 seem. In some embodiments, a plasma comprises ethylene having a flow rate of less than or equal to 32 seem, less than or equal to 30 seem, less than or equal to 28 seem, less than or equal to 26 seem, less than or equal to 24 seem, less than or equal to 22 seem, less than or equal to 20 seem, less than or equal to 18 seem, less than or equal to 16 seem, less than or equal to 14 seem, less than or equal to 12 seem, less than or equal to 10 seem, less than or equal to 9 seem, less than or equal to 8 seem, less than or equal to 7 seem, less than or equal to 6 seem, less than or equal to 5 seem, or less than or equal to 4 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 4 seem and less than or equal to 32 seem, greater than or equal to 8 seem and less than or equal to 24 seem, or greater than or equal to 12 seem and less than or equal to 16 seem). Other ranges are also possible.

[0146] A plasma described herein may comprise ammonia having any of a variety of suitable flow rates. In some embodiments, a plasma comprises ammonia having a flow rate of greater than or equal to 4 seem, greater than or equal to 8 seem, greater than or equal to 12 seem, greater than or equal to 16 seem, greater than or equal to 20 seem, greater than or equal to 24 seem, greater than or equal to 28 seem, greater than or equal to 32 seem, greater than or equal to 36 seem, greater than or equal to 40 seem, greater than or equal to 44 seem, greater than or equal to 48 seem, greater than or equal to 52 seem, greater than or equal to 56 seem, or greater than or equal to 60 seem. In some embodiments, a plasma comprises ammonia having a flow rate of less than or equal to 64 seem, less than or equal to 60 seem, less than or equal to 56 seem, less than or equal to 52 seem, less than or equal to 48 seem, less than or equal to 44 seem, less than or equal to 40 seem, less than or equal to 36 seem, less than or equal to 32 seem, less than or equal to 28 seem, less than or equal to 24 seem, less than or equal to 20 seem, less than or equal to 16 seem, or less than or equal to 12 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 4 seem and less than or equal to 64 seem, greater than or equal to 8 seem and less than or equal to 32 seem, or greater than or equal to 12 seem and less than or equal to 24 seem). Other ranges are also possible.

[0147] A plasma described herein may comprise carbon dioxide having any of a variety of suitable flow rates. In some embodiments, a plasma comprises carbon dioxide having a flow rate of greater than or equal to 8 seem, greater than or equal to 16 seem, greater than or equal to 24 seem, greater than or equal to 32 seem, greater than or equal to 40 seem, greater than or equal to 48 seem, greater than or equal to 56 seem, greater than or equal to 64 seem, greater than or equal to 72 seem, greater than or equal to 80 seem, greater than or equal to 88 seem, greater than or equal to 96 seem, greater than or equal to 104 seem, greater than or equal to 112 seem, or greater than or equal to 120 seem. In some embodiments, a plasma comprises carbon dioxide having a flow rate of less than or equal to 128 seem, less than or equal to 120 seem, less than or equal to 112 seem, less than or equal to 104 seem, less than or equal to 96 seem, less than or equal to 88 seem, less than or equal to 80 seem, less than or equal to 72 seem, less than or equal to 64 seem, less than or equal to 56 seem, less than or equal to 48 seem, less than or equal to 40 seem, less than or equal to 32 seem, or less than or equal to 24 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 8 seem and less than or equal to 128 seem, greater than or equal to 16 seem and less than or equal to 96 seem, or greater than or equal to 32 seem and less than or equal to 64 seem). Other ranges are also possible.

[0148] A plasma described herein may comprise hexamethyldisiloxane having any of a variety of suitable flow rates. In some embodiments, a plasma comprises hexamethyldisiloxane having a flow rate of greater than or equal to 8 seem, greater than or equal to 10 seem, greater than or equal to 12 seem, greater than or equal to 14 seem, greater than or equal to 16 seem, greater than or equal to 18 seem, greater than or equal to 20 seem, greater than or equal to 24 seem, greater than or equal to 28 seem, greater than or equal to 32 seem, greater than or equal to 36 seem, greater than or equal to 40 seem, or greater than or equal to 44 seem. In some embodiments, a plasma comprises hexamethyldisiloxane having a flow rate of less than or equal to 48 seem, less than or equal to 44 seem, less than or equal to 40 seem, less than or equal to 36 seem, less than or equal to 32 seem, less than or equal to 28 seem, less than or equal to 24 seem, less than or equal to 20 seem, less than or equal to 18 seem, less than or equal to 16 seem, less than or equal to 14 seem, less than or equal to 12 seem, or less than or equal to 10 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 8 seem and less than or equal to 48 seem, greater than or equal to 16 seem and less than or equal to 36 seem, or greater than or equal to 24 seem and less than or equal to 32 seem). Other ranges are also possible. A plasma described herein may comprise oxygen having any of a variety of suitable flow rates. In some embodiments, a plasma comprises oxygen having a flow rate of greater than or equal to 20 seem, greater than or equal to 24 seem, greater than or equal to 28 seem, greater than or equal to 32 seem, greater than or equal to 36 seem, greater than or equal to 40 seem, greater than or equal to 44 seem, greater than or equal to 48 seem, greater than or equal to 52 seem, greater than or equal to 56 seem, or greater than or equal to 60 seem. In some embodiments, a plasma comprises oxygen having a flow rate of less than or equal to 64 seem, less than or equal to 60 seem, less than or equal to 56 seem, less than or equal to 52 seem, less than or equal to 48 seem, less than or equal to 44 seem, less than or equal to 40 seem, less than or equal to 36 seem, less than or equal to 32 seem, less than or equal to 28 seem, or less than or equal to 24 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 20 seem and less than or equal to 64 seem, greater than or equal to 32 seem and less than or equal to 56 seem, or greater than or equal to 40 seem and less than or equal to 52 seem). Other ranges are also possible.

[0149] A plasma described herein may comprise argon having any of a variety of suitable flow rates. In some embodiments, a plasma comprises argon having a flow rate of greater than or equal to 2 seem, greater than or equal to 4 seem, greater than or equal to 6 seem, greater than or equal to 8 seem, greater than or equal to 10 seem, greater than or equal to 12 seem, greater than or equal to 14 seem, greater than or equal to 16 seem, greater than or equal to 18 seem, greater than or equal to 20 seem, or greater than or equal to 22 seem. In some embodiments, a plasma comprises argon having a flow rate of less than or equal to 24 seem, less than or equal to 22 seem, less than or equal to 20 seem, less than or equal to 18 seem, less than or equal to 16 seem, less than or equal to 14 seem, less than or equal to 12 seem, less than or equal to 10 seem, less than or equal to 8 seem, or less than or equal to 6 seem. Combinations of these ranges are also possible (e.g., greater than or equal to 2 seem and less than or equal to 24 seem, greater than or equal to 6 seem and less than or equal to 18 seem, or greater than or equal to 10 seem and less than or equal to 16 seem). Other ranges are also possible.

[0150] A face mask described herein may have any of a variety of suitable bacterial filtration efficiencies. In some embodiments, a face mask has a bacterial filtration efficiency of greater than or equal to 90%, greater than or equal to 91%, greater than or equal to 92%, greater than or equal to 93%, greater than or equal to 94%, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, or greater than or equal to 99.5%. In some embodiments, a face mask has a bacterial filtration efficiency of less than or equal to 99.9%, less than or equal to 99.5%, less than or equal to 99%, less than or equal to 98%, less than or equal to 97%, less than or equal to 96%, less than or equal to 95%, less than or equal to 94%, less than or equal to 93%, less than or equal to 92%, or less than or equal to 91%. Combinations of these ranges are also possible (e.g., greater than or equal to 90% and less than or equal to 99.9%, greater than or equal to 95% and less than or equal to 99.9%, or greater than or equal to 98% and less than or equal to 99.9%). Other ranges are also possible.

[0151] The bacterial filtration efficiency may be determined using ASTM F2101-19. Briefly, a face mask material is clamped between a collection impactor and an aerosol chamber, according to some embodiments. Staphylococcus aureus may then be introduced into the aerosol chamber and a bacterial aerosol was created using a nebulizer. The aerosol may then be drawn through the medical face mask material using a vacuum attached to the cascade impactor. Any aerosol droplets that penetrate the medical face mask material may be collected by a six-stage cascade impactor. An upstream bacterial particle count may then be determined by using a control with no filtrating face mask material. Downstream particles may be collected by the impactor, incubated for a period of time (e.g., 48 h), and counted to determine the number of bacterial particles collected. A ratio of the upstream counts to the downstream counts collected for the test specimen may be calculated and reported as a percent bacterial filtration efficiency.

[0152] A face mask described herein may have any of a variety of suitable sub-micron filtration efficiencies. In some embodiments, a face mask has a sub-micron filtration efficiency of greater than or equal to 90%, greater than or equal to 91%, greater than or equal to 92%, greater than or equal to 93%, greater than or equal to 94%, greater than or equal to 95%, greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, or greater than or equal to 99.5%. In some embodiments, a face mask has a sub-micron filtration efficiency of less than or equal to 99.9%, less than or equal to 99.5%, less than or equal to 99%, less than or equal to 98%, less than or equal to 97%, less than or equal to 96%, less than or equal to 95%, less than or equal to 94%, less than or equal to 93%, less than or equal to 92%, or less than or equal to 91%. Combinations of these ranges are also possible (e.g., greater than or equal to 90% and less than or equal to 99.9%, greater than or equal to 95% and less than or equal to 99.9%, or greater than or equal to 98% and less than or equal to 99.9%). Other ranges are also possible.

[0153] The sub-micron filtration efficiency may be determined using ASTM F2299. Briefly, a face mask may be placed in the path of the air flow inside an filter testing apparatus (e.g., a ATI 100X filter testing apparatus), and a good seal may be ensured between the membrane's edges and the outlet of the air flow. Aerosolized sodium chloride may then be injected into an air stream flowed through the mask. Face velocity, upstream and downstream particle counts, and upstream and downstream air flows may be measured. The sub-micron filtration efficiency may be conducted with test equipment (e.g., TSI or equivalent) set to meet the following parameters: the NaCl aerosol has a size distribution with count median diameter (CMD) of 0.075 ± 0.020 pm and a standard geometric deviation (SGD) not exceeding 1.86. The particles may be neutralized to the Boltzmann equilibrium state. The mask may be tested at a flow rate of 60 L / min ± 4 L / min. The entire mask may be sealed for testing to prevent leakage. The environmental temperature may be 25 ± 5 °C and the relative humidity may be 30 ± 10 %.

[0154] A face mask described herein may have any of a variety of suitable pressure drops. In some embodiments, a face mask has a pressure drop of greater than or equal to 1 mmFhO, greater than or equal to 1.5 mmFhO, greater than or equal to 2 mmFhO, greater than or equal to 2.5 mmFhO, greater than or equal to 3 mmFhO, greater than or equal to 3.5 mmFhO, greater than or equal to 4 mmFhO, greater than or equal to 4.5 mmFhO, greater than or equal to 5 mmFhO, greater than or equal to 5.5 mmFhO, greater than or equal to 6 mmFhO, greater than or equal to 6.5 mmFhO, greater than or equal to 7 mmFhO, or greater than or equal to 7.5 mmFhO. In some embodiments, a face mask has a pressure drop of less than or equal to 8 mmFhO, less than or equal to 7.5 mmFhO, less than or equal to 7 mmFhO, less than or equal to 6.5 mmFhO, less than or equal to 6 mmFhO, less than or equal to 5.5 mmFhO, less than or equal to 5 mmFhO, or less than or equal to 4.5 mmFhO. Combinations of these ranges are also possible (e.g., greater than or equal to 1 mmFhO and less than or equal to 8 mmFhO, greater than or equal to 4 rnrnH O and less than or equal to 7 mmthO, greater than or equal to 5 mmthO and less than or equal to 7 mmthO, or greater than or equal to 6 mmthO and less than or equal to 7 mmthO). Other ranges are also possible. The pressure drop may be determined using ASTM F2299, as described above.

[0155] Another advantage of the transparent face masks described herein is that, according to some embodiments, they have a relative high ability to transmit sound. For example, in some embodiments, a tone transmitted through a face mask has a relatively low attenuation relative to an identical tone transmitted from the same source without the face mask. In some embodiments, a tone transmitted through a face mask is attenuated by less than or equal to, less than or equal to 9 dB, less than or equal to 8 dB, less than or equal to 7 dB, less than or equal to 6 dB, less than or equal to 5 dB, less than or equal to 4 dB, less than or equal to 3 dB, or less than or equal to 2 dB. In some embodiments, a tone transmitted through a face mask is attenuated by greater than or equal to 1 dB, greater than or equal to 2 dB, greater than or equal to 3 dB, greater than or equal to 4 dB, greater than or equal to 5 dB, greater than or equal to 6 dB, greater than or equal to 7 dB, greater than or equal to 8 dB, or greater than or equal to 9 dB. Combinations of these ranges are also possible (e.g., greater than or equal to 1 dB and less than or equal to 10 dB, greater than or equal to 1 dB and less than or equal to 6 dB, greater than or equal to 3 dB and less than or equal to 5 dB, or greater than or equal to 3 dB and less than or equal to 4 dB). Other ranges are also possible.

[0156] The attenuated tone may have any of a variety of appropriate frequencies. For example, in some embodiments, an attenuated tone has a frequency of greater than or equal to 20 Hz, greater than or equal to 50 Hz, greater than or equal to 100 Hz, greater than or equal to 150 Hz, greater than or equal to 200 Hz, greater than or equal to 500 Hz, greater than or equal to 1,000 Hz, greater than or equal to 2,000 Hz, greater than or equal to 3,000 Hz, greater than or equal to 4,000 Hz, greater than or equal to 5,000 Hz, greater than or equal to 6,000 Hz, greater than or equal to 7,000 Hz, greater than or equal to 8,000 Hz, greater than or equal to 9,000 Hz, greater than or equal to 10,000 Hz, greater than or equal to 12,000 Hz, greater than or equal to 14,000 Hz, greater than or equal to 16,000 Hz, or greater than or equal to 18,000 Hz. In some embodiments, an attenuated tone has a frequency of less than or equal to 20,000 Hz, less than or equal to 18,000 Hz, less than or equal to 16,000 Hz, less than or equal to 14,000 Hz, less than or equal to 12,000 Hz, less than or equal to 10,000 Hz, less than or equal to 9,000 Hz, less than or equal to 8,000 Hz, less than or equal to 7,000 Hz, less than or equal to 6,000 Hz, less than or equal to 5,000 Hz, less than or equal to 4,000 Hz, less than or equal to 3,000 Hz, less than or equal to 2,000 Hz, less than or equal to 1,000 Hz, less than or equal to 500 Hz, less than or equal to 500 Hz, less than or equal to 200 Hz, or less than or equal to 150 Hz. Combinations of these ranges are also possible (e.g., greater than or equal to 20 Hz and less than or equal to 20,000 Hz, greater than or equal to 150 Hz and less than or equal to 10,000 Hz, or greater than or equal to 500 Hz and less than or equal to 10,000 Hz). Other ranges are also possible.

[0157] The attenuation of the tone may be determined in an anechoic chamber by the following procedure. A tone may be generated by a head and torso simulator (e.g., a GRAS head and torso simulator) that plays white noise through the artificial mouth (KEMAR 45BC or equivalent manikin with mouth simulator and loudspeaker), with or without a face mask. An output acoustic signal may be measured and recorded by a microphone located at 6 ft distance from the loudspeaker. The attenuation may be measured as the drop in sensed sound intensity when the mask is used, relative to a sound intensity sensed without the mask.

[0158] In a particular set of embodiments, the face mask attenuates a tone by less than or equal to 10 dB, less than or equal to 6 dB, less than or equal to 5 dB, or less than or equal to 4 dB for a tone having a frequency between or equal to 20 Hz and 20,000 Hz, 150 Hz and 10,000 Hz, for a tone generated by a head and torso simulator with a loudspeaker located 6 ft from a recording microphone, relative to the intensity of the tone in the absence of the face mask.

[0159] In some embodiments, a face mask described herein is resistant to flame spread. Flame spread resistance may be measured by the test method outlined in 16 CFR Part 1610 (2008). Briefly, a face mask material may be mounted at an angle in a chamber. Near the top of the material, a weighted thread may be configured to fall when the weighted thread is burned. A flame may be brought close to the bottom of the face mask material to ignite the face mask material for 1.0 seconds. A material is resistant to flame spread if the ignition of the bottom of the face mask does not bum the weighted thread, causing the weight to fall. In some embodiments, a face mask described herein is biocompatible. A face mask may be biocompatible if it has a relatively low minimal essential media elution (MEM) score. In some embodiments, the face mask has a MEM score of greater than or equal to 0, greater than or equal to 1, greater than or equal to 2, greater than or equal to 3. The score may be less than or equal to 4, or less than or equal to 3. Combinations of the above-referenced ranges are also possible (e.g., greater than or equal to 0 and less than or equal to 4). In some embodiments, the face mask has a MEM score of exactly 0.

[0160] The MEM score may be determined using ANSVAAMVISO 10993-5. Briefly, an extract of the face mask may be prepared by agitation of the face mask in MEM with 5% bovine serum for 24 hours at 37 degrees. The extract of the face mask may then be added to industry standard L-929 (ATCC CCL-1) cell monolayers and incubated for 72 hours at 37 degrees and 5% CO2. The cell monolayers may be examined and scored based on the degree of cellular destruction to determine the MEM score.

[0161] In one aspect, a method of making a face mask is provided. According to some embodiments, the method of making a face mask comprises obtaining a first, support layer and depositing a second, filtration layer on top of the first, support layer. The second layer may be deposited by any of a variety of appropriate methods. For example, the second layer (e.g., a filtration layer) may be supported by electrospinning (e.g., melt electrospinning or solvent electrospinning). A third, support layer may be deposited on the second, filtration layer using any of a variety of appropriate methods. For example, the third, support layer may be laminated (e.g., heat-laminated, adhesive-laminated) on top of the second, filtration layer. The resulting structure, comprising the first, support layer, the second, filtration layer, and the third, support layer may then be formed into a face mask by any of a variety of appropriate methods.

[0162] In another aspect, a method of making a face mask is provided. According to some embodiments, a face mask is made by obtaining a first, support layer and depositing a second, filtration layer on top of the first, support layer to produce a first bilayered article. In some embodiments, a face mask is made by obtaining a third, support layer and depositing a fourth, filtration layer on the third, support layer to produce a second bi-layered article. The second bi-layered article may then be deposited on the first bi-layered article such that the second, filtration layer and the fourth, filtration layer are disposed between the first, support layer and the third, support layer. The second bi- layered article may be deposited on the first bi-layered article by any of a variety of appropriate methods. For example, the second bi-layered article may be laminated to the first bi-layered article. In some embodiments, the bi-layered articles are laminated directly together, leaving an interface between the second, filtration layer and the fourth, filtration layer. According to some embodiments, the bi-layered articles are laminated using an adhesive, leaving an adhesive disposed between the second, filtration layer and the fourth, filtration layer. In some embodiments, a fifth, separation layer is obtained and the bi-layered articles are laminated together such that the fifth, separation layer is disposed between and separates the second, filtration layer and the fourth, filtration layer. The resulting structure may then be formed into a face mask by any of a variety of appropriate methods.

[0163] In some embodiments, the face mask is produced and used without heating. It has been recognized that heating may melt the fibers of a fiber web (e.g., a fiber web of a first layer, a second layer, a third layer, a fourth layer), producing a fused- fiber structure, according to some embodiments. Without wishing to be bound by any particular theory, the fused fiber structure may improve mechanical strength of a fiber web, but may also increase the scattering from the fused fiber structure. This may result in an undesirably low transparency in some, but not necessarily all embodiments.

[0164] According to some embodiments, after the structure comprising the first, support layer, the second, filtration layer, and the third, support layer has been formed, it can be treated, such that it has a hydrophobic surface and / or a hydrophilic surface. The face mask may, in some embodiments, be produced such that an external surface of the face mask (e.g., a surface facing outward from a face of a wearer, during use) is hydrophobic, as discussed above. The face mask may, in some embodiments, be produced such that an internal surface of the face mask (e.g., a surface facing inward, towards a face of a wearer during use) is hydrophilic.

[0165] Advantages have been recognized to folding the face masks and / or articles provided herein in particular ways and / or to have particular pleated or folded configurations, according to some embodiments. In some embodiments, for example, a face mask (or an article suitable for use in a face mask) is folded (e.g., so that its final configuration is pleated) such that it can be more readily or conformally contoured against a curved surface, such as curved facial features. For example, such a face mask may comprise one or more pleats that, when the face mask is worn, at least partially unfold to allow the face mask to better conform to the curves and features of the face of a wearer.

[0166] Certain embodiments of the masks provided herein may have any suitable number of pleats. In some embodiments, a face mask comprises greater than or equal to

[0167] 1 pleat, greater than or equal to 2 pleats, greater than or equal to 3 pleats, or greater than or equal to 4 pleats. In some embodiments, a face mask comprises less than or equal to 5 pleats, less than or equal to 4 pleats, less than or equal to 3 pleats, or less than or equal to

[0168] 2 pleats. Combinations of these ranges are also possible (e.g., greater than or equal to 1 pleat and less than or equal to 5 pleats, or greater than or equal to 2 pleats and less than or equal to 3 pleats). Other ranges are also possible.

[0169] Conventionally, face masks are pleated with three pleats. However, it has now been determined and is herein first disclosed that in the context of transparent face masks as provided herein, certain advantages are gained by using only two pleats. In particular, it has been determined that conventional, three-pleated face masks typically include a pleat that is positioned over or in close proximity to the mouth of a mask wearer when in use. In such designs, the extra layers of filter material associated with such a pleat positioned over or in close proximity to the mouth of a mask wearer tends to reduce the transmission of light through the pleat, relative to the transmission of light through a single-layered, non-folded portion of the transparent face mask and / or otherwise visually distort or render less visible the mouth of the wearer. In the context of a transparent face mask, the use of two pleats rather than three better facilitates pleats to be offset from the mouth of the wearer while still providing adequate flexibility and conformal face coverage, thus allowing clearer optical transmission and visualization of the wearer’s facial expressions through the transparent mask by aligning the wearer’s mouth with a non-folded / pleated portion of the face mask. Thus, it has been determined and now disclosed herein that the use of exactly two pleats can enhance the performance of transparent face masks by providing a benefit that would not be relevant to or apparent to the skilled person from the context of designs for multi-pleated opaque face masks.

[0170] FIGS. 6A-6B show a schematic illustration of a non-limiting, two-pleated face mask, according to some embodiments. FIG. 6A shows a top-view of a side of a two- pleated face mask 601 that would not be in contact with the wearer’s face, laid flat. Mask 601 comprises filter material 602 comprising two pleats 603. Mask 601 is laminated to nose strip 605 and ear loops 607. FIG. 6B shows a perspective, schematic illustration of mask 601, contoured as it would be when worn. As shown, portion 611 of face mask 601 between pleats 603, which would rest over a wearer’s mouth, is not pleated and would thus provide improved visual clarity of the wearer’s facial expression relative to a conventional three-pleated design.

[0171] FIG. 7 presents a photograph of a non-limiting two-pleated transparent mask 701 contoured around a sculpted head 725 (black form). As shown, mask 701 is transparent, permitting observation of sculpted head 725 through mask 701. Pleated portion 703 results in multi-layered filter material that visually obscures / distorts visualization of the portion of sculpted head 725 that it overlays, resulting in a whiter coloration and greater opacity. However, with the two-pleated design shown, this pleated, multilayer portion does not overlay the mouth of the wearer, and rather a single-layer portion 711 of mask 701 is not pleated is positioned to cover the mouth of a wearer.

[0172] A face mask may be pleated using any of a variety of suitable conventional methods known to the skilled artisan, and the disclosure is not limited to any particular pleating method or manufacturing equipment. In some embodiments, for example, the mask is configured to be pleated using a pleat-roller in a conventional pleating machine. FIG. 8 presents a photograph of a non-limiting pleat-roller 801 that is configured to form two pleats, e.g. as illustrated above in the embodiment shown in FIGS. 6A, 6B, and 7, in filter material used to form masks. The pleats can be formed, for example using a pleat forming roller(s) 801 including two pleat- forming flange portions 803 and 805 position in a pleat forming machine for face mask filter media (for example a Medical Mask Machine available from RDI Medical, Itasca, IL USA).

[0173] The following examples are intended to illustrate certain embodiments of the present disclosure, but do not exemplify the full scope of the disclosure.

[0174] EXAMPLE 1

[0175] This example describes the preparation and properties of a non-limiting facemask, according to some embodiments. In this example, an article was prepared. The article was prepared using a first, support layer comprising a Nylon / PLA mesh. A second, filtration layer of the article was electrospun on top of the first, support layer, the second, filtration layer comprising fibers with an average diameter of greater than or equal to 100 nm and less than or equal to 280 nm. A third, support layer comprising a Nylon / PLA mesh was laminated such that the second layer was disposed between the first layer and the third layer. A nose strip was laminated onto the article, and the article was folded to include pleats. A side of the article was laminated to preserve the folded pleats, and ear loops were laminated onto the article. The resulting article was a face mask with a high optical transparency.

[0176] The bacterial filtration efficiency (BFE) of the article was tested using the ASTM F2101-19 standard with a BFE flow rate of 28.3 L / min. The challenge delivery was 1.7xl03- 3.0xl03colony CFU with an MPS of 3.0 ± 0.3 microns. Submicron particulate filtration efficiency and pressure drop for the samples were also measured, using a sodium chloride aerosol with a particle size distribution with a count median diameter of 0.075 ± 0.020 microns and a standard geometric deviation not exceeding 1.86. The flow rate was 60 L / min ± 4 L / min at a temperature of 25 °C ± 5 °C and a relative humidity of 30% ± 10%. Five replicates (labeled Replicate 1, Replicate 2, Replicate 3, Replicate 4, and Replicate 5) were performed for each experiment. Table 1 presents the results of these experiments.

[0177] Table 1. Filtration properties of non-limiting articles.

[0178] As shown in Table 1, the articles functioned as excellent face masks, with high bacterial and particulate filtration efficiencies. Additional safety tests were performed on the articles, demonstrating good flame resistance and safety. Flame spread tests indicated that all five articles immediately extinguished upon ignition. And the articles were tested for biocompatibility using ISO ANSI / AAMI / ISO 10993-5, exhibiting a MEM score of 0, thereby demonstrating that the masks were cytocompatible. Collectively, these results demonstrate the fabrication exemplary useful properties of non-limiting face masks prepared by a method described herein.

[0179] EXAMPLE 2

[0180] In this example, two cuts of non-limiting, transparent face masks were tested for their ability to transmit sound. The masks were compared with a commercial 4-ply and N95 mask, to determine which masks transmitted sound most effectively. The face masks of this example were prepared using articles fabricated by the process described in Example 1. Two transparent face masks (“Transparent Mask 1” and “Transparent Mask 2”) were prepared, having different cuts. The sound transmission was determined in an anechoic chamber by generating a tone may using a GRAS head and torso simulator that played white noise through the artificial mouth (KEMAR 45BC or equivalent manikin with mouth simulator and loudspeaker), with or without a face mask. An output acoustic signal was measured and recorded by a microphone located at 6 ft distance from the loudspeaker. The attenuation was measured as the drop in sensed sound intensity when the mask is used, relative to a sound intensity sensed without the mask. The frequency of the tone was varied systematically across the range of audible frequencies.

[0181] FIG. 5 presents the attenuation associated with each of the face masks. As shown, attenuation over the audible range was generally lower for the transparent face masks, and typically stayed below a 6 dB attenuation threshold that has been set as a desired industry standard, outperforming both the N95 and the commercial 4-ply masks. This result demonstrates the improved sound transmission through non-limiting transparent face masks as described herein.

[0182] EXAMPLE 3

[0183] In this example, a non-limiting article, with a hydrophobic and a hydrophilic internal surface was prepared. The article was prepared as described in Example 1, but the first layer was plasma treated to increase its hydrophobicity, and the third layer was plasma-treated to increase its hydrophilicity, using plasmas as described above. Untreated, the first and third layers were observed to have a water contact angle of 103.5°. However, after plasma treatment, the first layer had a water contact angle of 131.7°, and the third layer had a water contact angle of 37.5°. This demonstrates the efficacy of the plasma treatments described above for fabrication of face masks with water- and blood-repellant external surfaces and anti-fogging, hydrophilic internal surfaces.

[0184] EXAMPLE 4

[0185] In this example an exemplary configuration of a two-pleated transparent face mask was prepared. The face mask was prepared from materials and using fabrication methods as generally described above in Example 1. A nose strip was laminated onto the article, and the article was pleated using a two -pleat-roller of the type pictured in FIG. 8. A side of the article was laminated to preserve the folded pleats, and ear loops were laminated onto the article. The resulting article was a two-pleated face mask with a high optical transparency. The exemplary two-pleated mask had the appearance illustrated schematically in FIGS. 6A-6B and the appearance shown in the photograph depicted in FIG. 7. FIG. 9 shows the dimensions of the two-pleated design of the formed mask 601. As shown in FIG. 9, mask 601 had width W1 = 174 mm and height Hl = 98 mm. Mask 601 also had nose-strip of width W2 = 94 mm and height H2 = 4 mm. The laminated portions of the mask, indicated by the dots 900 formed by the lamination process, had a perimetric thickness XI = 15 mm along the sides of the mask, X2 = 14 mm along the bottom of the mask, and X3 = 20 mm along the top of the mask. Elastic ear loops 607 had a relaxed length of 200 mm each. Pleats 603 are positioned on the face covering region 611 of the mask to provide pleat widths Z1 = 18 mm (top pleat width), and Z2 = 17 mm (bottom pleat width) when mask 601 is laid flat as shown in FIG. 9. The pleats are separated from one another by distance Y = 27 mm.

[0186] The resulting mask is pleated such that the pleats do not cover the mouth of the wearer when in use by a typical wearer, thus providing the appearance and communication advantages of two-pleated designs for transparent masks described above.

[0187] While several embodiments of the present disclosure have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the functions and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the present disclosure. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the teachings of the present disclosure is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the disclosure described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the disclosure may be practiced otherwise than as specifically described and claimed. The present disclosure is directed to each individual feature, system, article, material, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and / or methods, if such features, systems, articles, materials, and / or methods are not mutually inconsistent, is included within the scope of the present disclosure.

[0188] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0189] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0190] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0191] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0192] As used herein, “wt%” is an abbreviation of weight percentage. As used herein, “at%” is an abbreviation of atomic percentage.

[0193] Some embodiments may be embodied as a method, of which various examples have been described. The acts performed as part of the methods may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include different (e.g., more or less) acts than those that are described, and / or that may involve performing some acts simultaneously, even though the acts are shown as being performed sequentially in the embodiments specifically described above.

[0194] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements. In the claims, as well as in the specification above, all transitional phrases such as

[0195] “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMSWhat is claimed is:

1. A transparent face mask, comprising: a first, support layer; a second, filtration layer adjacent to the first layer, wherein the second layer comprises a plurality of fibers having an average diameter of greater than or equal to 100 nm and less than or equal to 280 nm; and a third, support layer, situated such that the second layer is disposed between the first layer and the third layer; wherein the transparent face mask has an optical transparency of greater than or equal to 50% at a region of overlap between the first, second, and third layer, for a wavelength of light, wherein the wavelength of light is greater than or equal to 300 nm and less than or equal to 720 nm; and wherein a surface of the transparent face mask is hydrophobic.

2. The transparent face mask of claim 1, further comprising a fourth, filtration layer disposed between the second layer and the third layer such that the fourth layer is disposed between the second layer and the third layer.

3. The transparent face mask of any preceding claim, wherein the first layer is directly adjacent to the second layer.

4. The transparent face mask of any one of claims 2-3, wherein the fourth layer is directly adjacent to the second layer.

5. The transparent face mask of any preceding claim, wherein the hydrophobicity rank of the hydrophobic surface is greater than or equal to 4 when measured using AATCC TM 193-2017.

6. The transparent face mask of any preceding claim, wherein the oil rank of the hydrophobic surface is greater than or equal to 2 when measured using AATCC TM 118-7. The transparent face mask of any preceding claim, wherein the surface of the transparent face mask comprises a coating layer and / or a plurality of nanostructures.

8. The transparent face mask of any preceding claim, wherein the surface of the transparent face mask is a first surface, and wherein a second surface of the transparent face mask is hydrophilic.

9. A transparent face mask, comprising: a first, support layer; a second, filtration layer adjacent to the first layer, wherein the second layer comprises a plurality of fibers having an average diameter of greater than or equal to 100 nm and less than or equal to 280 nm; and a third, support layer, situated such that the second layer is disposed between the first layer and the third layer; wherein the transparent face mask has an optical transparency of greater than or equal to 50% at a region of overlap between the first, second, and third layer, for a wavelength of light, wherein the wavelength of light is greater than or equal to 300 nm and less than or equal to 720 nm; and wherein a surface of the transparent face mask is hydrophilic.

10. The transparent face mask of claim 9, further comprising a fourth, filtration layer disposed between the second layer and the third layer such that the fourth layer is disposed between the second layer and the third layer.

11. The transparent face mask of any one of claims 9-10, wherein the first layer is directly adjacent to the second layer.

12. The transparent face mask of any one of claims 10-11, wherein the fourth layer is directly adjacent to the second layer.

13. The transparent face mask of any preceding claim, wherein the water contact angle of the hydrophilic surface is greater than or equal to 10°.

14. The transparent face mask of any preceding claim, wherein the surface of the transparent face mask comprises a coating layer.

15. A transparent face mask, comprising: a first, support layer; and a second, filtration layer adjacent to the first layer, wherein the transparent face mask has an optical transparency of greater than or equal to 50% at a region of the face mask, wherein the wavelength of light is greater than or equal to 300 nm and less than or equal to 720 nm; and wherein the transparent face mask has exactly two pleats.

16. The transparent face mask of claim 15, further comprising a third, support layer, situated such that the second layer is disposed between the first layer and the third layer.

17. The transparent face mask of any one of claims 15-16, wherein the second, filtration layer comprises a plurality of fibers.

18. The transparent face mask of any one of claims 16-17, wherein the region of the face mask is a region of overlap between the first, second, and third layer, for a wavelength of light19. The transparent face mask of any one of claims 16-18, further comprising a fourth, filtration layer disposed between the second layer and the third layer such that the fourth layer is disposed between the second layer and the third layer.

20. The transparent face mask of any one of claims 15-19, wherein the first layer is directly adjacent to the second layer.

21. The transparent face mask of any one of claims 15-20, wherein the fourth layer is directly adjacent to the second layer.

22. The transparent face mask of any preceding claim, wherein the face mask has a bacterial filtration efficiency of greater than or equal to 90% when measured using ASTM F2101-19.

23. The transparent face mask of any preceding claim, wherein the face mask has a sub micron particle filtration efficiency of greater than or equal to 90% when measured using ASTM F2299.

24. The transparent face mask of any preceding claim, wherein the face mask has a bacterial filtration efficiency of greater than or equal to 99.9% when measured using ASTM F2101-19.

25. The transparent face mask of any preceding claim, wherein the face mask has a sub micron particle filtration efficiency of greater than or equal to 99.9% when measured using ASTM F2299.

26. The transparent face mask of any preceding claim, wherein the face mask has not been melted.

27. The transparent face mask of any preceding claim, wherein the layer comprising the hydrophobic surface comprises a plurality of nanostructures.

28. The transparent face mask of any preceding claim, wherein the hydrophobic surface has been prepared by plasma treatment.

29. The transparent face mask of any preceding claim, wherein the hydrophilic surface has been prepared by plasma treatment.

30. The transparent face mask of any preceding claim, wherein the pressure drop across the mask is less than or equal to 7.5 mmTO.

31. The transparent face mask of any preceding claim, wherein the transparent face mask is compostable.

32. The transparent face mask of any preceding claim, wherein a tone having a frequency greater than or equal to 20 Hz and less than or equal to 20,000 Hz is attenuated by no more than 10 dB when the tone is transmitted from a source on a first side of the transparent face mask to a sensor on an opposite side of the transparent face mask.

33. The transparent face mask of any preceding claim, wherein the plurality of fibers having an average diameter of greater than or equal to 200 nm and less than or equal to 280 nm

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