Articles with re-entrant geometries and methods of making the same

Abstract

A method of making a master pattern includes forming a polymer mold comprising a pattern with a plurality of structures, each of the structures having a radius of 100 μm or less; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising the metal ions onto the pre-wetted conductive seed layer; and separating the electroformed metal from the polymer mold to form the master pattern.

Description

[0001] Articles with Re-Entrant Geometries and Methods of Making the Same

[0002] Cross-Reference to Related Application

[0003] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 530,416, filed August 2, 2023, which is incorporated herein by reference in its entirety.

[0004] Field

[0005] The present disclosure relates to articles with re-entrant geometries. The present disclosure further relates to methods of making articles with re-entrant geometries.

[0006] Summary

[0007] The present disclosure provides a method of making a master pattern includes forming a polymer mold comprising a pattern with a plurality of structures, each of the structures having a radius of 100 pm or less; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising the metal onto the pre-wetted release-layer; and separating the electroformed metal from the polymer mold to form the master pattern. The forming of the polymer mold may include coating a pre-master with a release layer; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare the polymer mold; and separating the polymer mold from the pre-master. Alternatively, the forming of the polymer mold may include embossing the pattern onto a thermoplastic blank. The radius of each of the plurality of structures may be 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less. The plurality of structures may include re-entrant structures. According to an embodiment, the master pattern comprises a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the premaster.

[0008] The present disclosure provides a master pattern made by a method including coating a pre-master with a release layer, the pre-master comprising a pattern comprising a plurality of structures having a radius of 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare a polymer mold; separating the polymer mold from the pre-master; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising the metal onto the pre-wetted release-layer; and separating the electroformed metal from the polymer mold to form the master pattern. The radius of each of the plurality of structures may be 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less. The plurality of structures may include re-entrant structures. According to an embodiment, the master pattern comprises a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

[0009] Brief Description of Figures

[0010] FIG. 1A is a schematic diagram illustrating the vertical contact line force of a droplet on a flat surface;

[0011] FIG. IB is a schematic diagram illustrating the vertical contact line force of droplets on a plurality of structures having a re-entrant geometry, in accordance with certain embodiments;

[0012] FIG. 1C is a diagram illustrating contact line force in accordance with certain embodiments;

[0013] FIG. 2A is a cross-sectional view of a sphere re-entrant geometry, in accordance with certain embodiments;

[0014] FIG. 2B is a cross-sectional view of an inverse sphere re-entrant geometry, in accordance with certain embodiments;

[0015] FIG. 2C is a cross-sectional view of a hoodoo re-entrant geometry, in accordance with certain embodiments;

[0016] FIG. 3 is a cross-sectional view of a master pattern structure having a hoodoo geometry showing various dimensions, in accordance with certain embodiments;

[0017] FIG. 4 is a cross-sectional perspective view of an article with a continuous hoodoo structure showing various dimensions, in accordance with certain embodiments; FIG. 5A is a schematic cross-sectional side view of a structure formed in accordance with certain embodiments;

[0018] FIG. 5B is a schematic cross-sectional side view of an inverse structure of FIG. 5 A;

[0019] FIG. 6A is a bottom perspective view of an article with a continuous lattice with reentrant hoodoo structures and drainage channels, in accordance with certain embodiments;

[0020] FIG. 6B is a cross-sectional side view of the continuous lattice of FIG. 6A;

[0021] FIG. 7A is a schematic cross-sectional side view of an article with a hoodoo re-entrant structure;

[0022] FIG. 7B is microscopic images of a master pattern with pre-wetting prior to electroforming according to embodiments of the present disclosure;

[0023] FIG. 7C is microscopic images of a mater pattern without pre-wetting prior to electroforming.

[0024] Definitions

[0025] All scientific and technical terms used herein have meanings commonly used in the art unless otherwise specified. The definitions provided herein are to facilitate understanding of certain terms used frequently herein and are not meant to limit the scope of the present disclosure.

[0026] Unless otherwise indicated, the terms “polymer” and “polymeric material” include, but are not limited to, organic homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc., and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to, isotactic, syndiotactic, and atactic symmetries.

[0027] The term “substantially” as used here has the same meaning as “significantly,” and can be understood to modify the term that follows by at least about 90 %, at least about 95 %, or at least about 98 %. The term “not substantially” as used here has the same meaning as “not significantly,” and can be understood to have the inverse meaning of “substantially,” i.e., modifying the term that follows by not more than 25 %, not more than 10 %, not more than 5 %, or not more than 2 %.

[0028] The term “about” is used here in conjunction with numeric values to include normal variations in measurements as expected by persons skilled in the art, and is understood to have the same meaning as “approximately” and to cover a typical margin of error, such as ±5 % of the stated value.

[0029] Terms such as “a,” “an,” and “the” are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration.

[0030] The terms “a,” “an,” and “the” are used interchangeably with the term “at least one.” The phrases “at least one of’ and “comprises at least one of’ followed by a list refers to any one of the items in the list and any combination of two or more items in the list.

[0031] As used here, the term “or” is generally employed in its usual sense including “and / or” unless the content clearly dictates otherwise. The term “and / or” means one or all of the listed elements or a combination of any two or more of the listed elements.

[0032] The recitations of numerical ranges by endpoints include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc. or 10 or less includes 10, 9.4, 7.6, 5, 4.3, 2.9, 1.62, 0.3, etc.). Where a range of values is “up to” or “at least” a particular value, that value is included within the range.

[0033] As used here, “have,” “having,” “include,” “including,” “comprise,” “comprising,” or the like are used in their open-ended sense, and generally mean “including, but not limited to.” It will be understood that “consisting essentially of,” “consisting of,” and the like are subsumed in “comprising” and the like. As used herein, “consisting essentially of,” as it relates to a composition, product, method, or the like, means that the components of the composition, product, method, or the like are limited to the enumerated components and any other components that do not materially affect the basic and novel character! stic(s) of the composition, product, method, or the like. The words “preferred” and “preferably” refer to embodiments that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the disclosure, including the claims.

[0034] Any direction referred to here, such as “top,” “bottom,” “left,” “right,” “upper,” “lower,” and other directions and orientations are described herein for clarity in reference to the figures and are not to be limiting of an actual device or system or use of the device or system. Devices or systems as described herein may be used in a number of directions and orientations.

[0035] Detailed Description

[0036] The present disclosure relates to articles with re-entrant geometries. The present disclosure further relates to methods of making articles with re-entrant geometries.

[0037] In some cases, it may be desirable to provide a material with the capability to resist contamination or to repel contamination by liquids. For example, it may be desirable for a material to repel liquids (such as polar liquids, e.g., water-based liquids, or non-polar liquids). Thus, depending on the intended use, a “contaminant” may be water or a water-based (aqueous) liquid or another polar liquid, or a non-polar liquid, such as an oil-based or organic- solvent-based liquid.

[0038] Generally, materials can provide a spectrum of liquid repellency properties ranging from non-repelling (i.e., liquid-philic) to repelling (i.e., liquid-phobic) and very repelling (i.e., superphobic). The degree of repellency can be determined by measuring a contact angle for the liquid with respect to the material. The contact angle is the angle measured through a liquid droplet where a liquid-vapor interface meets a solid surface. Liquid-phobic (e.g., hydrophobic and oleophobic) materials are defined as materials with a contact angle greater than 90°, and superhydrophobic materials have a contact angle greater than 150°. The liquid repellency of a surface is dictated by both the surface chemistry (surface energy) and surface structure. Embodiments described herein are directed to methods of making a master pattern that may be used to prepare materials with a modified surface structure to achieve increased repellency. Patterning a surface of a material with a plurality of specified structures can increase the repellency of the material. For example, a wetting material, such as a liquid-philic material could be made liquid-phobic by disposing a plurality of ordered structures on a surface of the material. In other examples, a hydrophobic material may be made oleophobic by disposing a plurality of structures on a surface of the material. This may be done by reducing, or avoiding, the use of coatings, and particularly by avoiding the use of coatings involving fluorine, such as environmentally unfriendly bio-persistent chemical coatings. While applying a predefined pattern to a material’s surface can improve hydrophobicity and oleophobicity, these repelling properties can be improved when the resulting surface involves a plurality of structures each having a re-entrant geometry. In some cases, surfaces of porous materials (such as a venting media or a filter media) may be made repellent by forming a plurality of structures on the surface of the porous material.

[0039] A re-entrant structure is any structure in which when a straight line is drawn through a portion of the structure, the line will cross through at least two interfaces of the structure. The re- entrancy may be defined relative to a plane. That is, a structure may be re-entrant relative to a horizontal plane (e.g., the plane of the substrate), where a line perpendicular to the horizontal plane (i .e., a vertical line), crosses through at least two interfaces of the structure. Re-entrant structures may be referred to as having re-entrant geometry. A structure may also be multiply reentrant. For example, a structure may be a double re-entrant. In a double re-entrant structure, a first line (e.g., a vertical line) drawn through a portion of the structure will cross through two interfaces of the structure, and there exists at least one second line, perpendicular to the first line, drawn through a portion of the structure that will cross through at least four interfaces of the structure.

[0040] A re-entrant structure may cause a meniscus of a liquid (e.g., droplet) to invert as a liquid wets into the material including the re-entrant structures. An inverted meniscus may reduce, minimize, or prevent the liquid from wetting through to the underlying surface. Similarly, a reentrant structure with a double re-entrant geometry has the above properties of a re-entrant geometry along with an overhang portion where the contact line of a liquid interface moves in a vertical direction on the overhang portion of the structure as the contact line moves along the surface. The inversion of a meniscus is illustrated in FIGS. 1A and IB. In FIG. 1A, a liquid droplet 106 is disposed in a gaseous environment 108 on a substantially flat surface of a substrate 102. The droplet adheres to the surface of the substrate 102, and the droplet’s 106 meniscus 104 curves outward, away from the substrate’s 102 surface, such that the vertical component, FCLV, of the contact line force, FCLis directed toward, or into, the substrate 102. The liquid has a contact angle 0 on the substrate 102. If the substrate 102 is a porous material, the droplet 106 may wet into and possibly occlude and clog any pores covered by the droplet 106. In FIG. IB, a plurality of structures 114A, 114B having a re-entrant geometry is disposed on the surface of the substrate 102. Here, the liquid droplet 106 adheres to the structures 114A, 114B and the meniscus 112 is inverted as compared with the meniscus 104. The inversion leaves a pocket of gas 108 between the droplet 106 and the surface of the substrate 102 between the structures 114A, 114B. This may be particularly desirable when the substrate 102 is a porous material, to maintain the porosity of the substrate 102. The vertical component of the contact line force, indicated by arrow FCLV. is also inverted to be directed away from substrate 102. The vertical component, FCLV, °f the contact line force, FCLis directed toward, or into, the structures 114 A, 114B.

[0041] The vertical component, FCLV, of the contact line force, FCL, is described by Equation 1 :

[0042] Equation 1 where yLGis the surface tension between the liquid and gas, I is the length of the contact line, 9 equilibrium is the contact angle at equilibrium described by Young’s equation (ysG = ysL + YLG cos Oequiiibrium, where S = solid, L = liquid, and G = gas) for a flat non-porous surface, and a is the angle the solid boundary makes with the horizontal plane, and the overbar represents that the sine function is averaged over all points in the contact line. The contact line is a continuous line at the interface of the liquid (e.g., droplet), the solid surface (e.g., the surface of the re-entrant structure), and the surrounding environment (e.g., air). When the forces affecting the liquid are at equilibrium, the contact line is pinned to the surface at a set of pinning points. At equilibrium, the contact line can be thought of as a continuous line that connects the pinning points along the perimeter of a droplet. The contact line force FCL and an inverted meniscus of a droplet 106 are further illustrated in FIG. 1C, also showing the tangent vector VT at a pinning location on the solid surface 114 and illustrating the angle a of the solid boundary with the horizontal plane (parallel to horizontal vector VH).

[0043] Certain re-entrant geometries can be used to invert a droplet’s meniscus. Such geometries are discussed further below.

[0044] FIGS. 2A-2C illustrate examples of various re-entrant structures that may be applied to a surface of a material. The re-entrant structures may have any suitable shape, size, pattern, and distance from each other (e.g., lattice pitch), as further discussed below. In some embodiments, the re-entrant structures may be applied in an ordered pattern. FIG. 2A illustrates a cross-section of a sphere geometry where the structures of a pattern are regularly spaced spheres 204 disposed on the surface of a porous material substrate 202. FIG. 2B illustrates a cross-section of an inverse sphere geometry where the structures 208 form a sphere-shaped void 206 among adjacent structures 208 on the surface of a substrate 202. While the structures in FIGS. 2A and 2B are shown as spheres (e.g., structure or void with a radius of a single length), the structures may also be modified to form three-dimensional ovals of various dimensions (e.g., structure or void having at least two radii of different lengths) or other shapes modified from a sphere. Hoodoos, for example in FIG. 2C, are a subcategory of re-entrant structures. A hoodoo generally has a stem-and-cap construction, where the cap is wider than the stem. FIG. 2C illustrates crosssections of re-entrant structures 210 having a hoodoo geometry, disposed on the surface of a substrate 202. The curved surfaces and overhanging configurations of each of these three geometries allow for the meniscus of a liquid to be flipped or inverted. An inverted meniscus may reduce, minimize, or prevent the liquid from wetting through to the underlying surface of the substrate 202.

[0045] Re-entrant structures may be formed using a variety of methods, including embossing, etching, additive manufacturing, and microfabrication. The formation method for creating reentrant structures may be selected based on the desired dimensions for the structures. Various methods for forming re-entrant structures are described below.

[0046] One example method involves microfabrication using a polymer substrate. First, the polymer substrate is provided. Next, a photoresist pattern is deposited on the substrate surface. Using a mixed gas reactive ion etching under the photoresist, the ring feature is formed in the polymer substrate. A material layer is deposited (e.g., sputter coated) on the surface to fill the ring feature. In certain embodiments, the material layer is a metal layer (e.g., nickel -chromium and gold) to provide adhesion and structural support. A photoresist is applied and the prior material layer is removed except for the portions protected by the photoresist. These portions form the re-entrant structure (e.g., hoodoo) caps. A mixed gas is used to reactive ion etch anisotropically to undercut the overhang portions of the hoodoo caps. A coating, such as parylene or another polymer, may optionally be applied to protect the structure and / or improve the omniphobicity of the structures. This method may be used to create a re-entrant structure where the stem and the cap are comprised of different materials. While the method may involve a polymer stem and a metal cap, a variety of material combinations may be used.

[0047] An alternative formation method uses microfabrication and molding. A molding material, such as a silicon wafer, may be patterned with photoresist and etched to form a mold. Next, an infill material is deposited into the mold and cured. For example, the infill material may be a polymer. Any portion of the infill material protruding from the mold may be optionally etched to further shape the hoodoo cap. As compared with the above-described method, this method may be used to form a hoodoo structure of a single material.

[0048] One example method involves fabricating a master pattern. Conventionally, master patterns have been fabricated, for example, by a subtractive method in which glass is etched by a femtosecond laser to form the re-entrant structure. The master pattern may also be formed by an additive method, e.g., using a 3D printer (e.g., two-photon lithography). Either a positive or negative master pattern may be fabricated with both approaches. The master pattern may further be replicated to fabricate robust stamps for further processing. Master patterns may either be directly replicated via electroforming to make multiple metal master patterns, or a polymer replica may be molded from the master pattern prior to electroforming. In either case, multiple metal master patterns may be electroformed to create a repository for further embossing processes. The replica pattern is then used in an embossing process to make the final re-entrant structure pattern. The master pattern may be used to mold or emboss materials with the pattern.

[0049] In order to make through-holes in a continuous re-entrant structure (e.g., as shown in FIG. 4), the master pattern may have a long pin that punctures through the polymer film during the embossing process. A sacrificial layer may be included on top of the polymer film in this case during the embossing process. Sphere and inverse sphere structures may be achieved with known deposition and etching processes.

[0050] As discussed above, one exemplary method for creating re-entrant structures in a material involves fabricating a master pattern. The master pattern, which is used to make the final reentrant structure, may be formed using a variety of methods. Typically, master patterns have been made by a fabrication process including multiple molding steps. First, a pre-master such as a glass master is provided. The pre-master can be fabricated, for example, by a subtractive method in which glass is etched by a femtosecond laser to form the re-entrant structure. Next, an infill material is deposited into the pre-master and cured to form a mold. For example, the infill material may be a polymer and the mold may be a polymer mold. The polymer mold may preserve the inverse features of the pre-master. The polymer mold may further be used to prepare the master pattern via electroforming. Either a positive or negative master may be fabricated with both approaches. In cases where the pattern is inverted, this first metal master can be used to create a final master pattern used for embossing. Once the master pattern is obtained, it may be used to make the final re-entrant structure by transferring features from the master pattern to make the final re-entrant structures. The master pattern should ideally preserve the original features from the pre-master to make the final re-entrant structures including the original designed features. Similarly, the master pattern should ideally preserve the inverse features from the polymer mold, as the polymer mold preserves the inverse features from the pre-master. However, during the master pattern fabrication, multiple replication or molding steps may increase the risk of degrading the features of the re-entrant structure, particularly when the features are small or when the features have a high aspect ratio of height to width (e.g., structures including a pin or similar feature). Especially during the electroforming, due to the repellent nature of re-entrant geometries and complex microscale features, the electroforming solution may not always penetrate and reach all the contours of the microscale features in the polymer mold. This may result in missing or defective features in the master pattern.

[0051] Thus, there is a need for an improved method of preparing master patterns. In particular, there is a need for an improved method of preparing master patterns by electroforming where an electroforming solution is able to penetrate and reach all the contours of the re-entrant structures. It would be desirable to provide a method for making a replica that preserves at least a 90 % replication of the re-entrant structures. Especially, there is a need for an electroforming method where an electroforming solution is able to reach and penetrate to all the contours of the polymer mold to make a master pattern that preserves at least a 90 % replication of the pattern of the premaster.

[0052] According to an embodiment, the methods of the present disclosure provide an improved method for preparing master patterns. The present disclosure provides a method for preparing master patterns by electroforming where an electroforming solution is able to reach and penetrate to all the contours of the re-entrant structures. The present disclosure provides a method for making a replica that preserves at least a 90 % replication of the re-entrant structures. The present disclosure provides an electroforming method where an electroforming solution is able to reach and penetrate to all the contours of the polymer mold to make a master pattern that preserves at least a 90 % replication of the pattern of the pre-master. The methods of the present disclosure are suitable for replicating structures that are small, e.g., 100 pm or less in radius. The methods of the present disclosure are suitable for replicating structures that include features with a high aspect ratio of height to width (e.g., an aspect ratio of 1 : 1 or greater, 1.3: 1 or greater, 1.5: 1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater, such as structures including a pin or similar feature). While there is no particular limit to the aspect ratio, in practice, the aspect ratio may be 10:1 or lower.

[0053] According to an embodiment, a method of making a master pattern includes forming a polymer mold and electroforming a metal onto the mold. The polymer mold may have a pattern with a plurality of structures. The polymer mold may have a pattern with a plurality of re-entrant structures. The structures may be relatively small. For example, each of the structures may have a radius of 100 pm or less. The structures may be or may include features with a high aspect ratio of height to width (e.g., an aspect ratio of 1 : 1 or greater, 1.3:1 or greater, 1.5:1 or greater, 2:1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater, such as a pin or similar feature). The method includes applying a conductive seed layer onto the polymer mold. The conductive seed layer may be or may include gold. The method further includes pre-wetting the conductive seed layer with a solvent prior to electroforming. Pre-wetting of the conductive seed layer may help the electroforming solution to reach all the contours of the pattern. After pre-wetting, the polymer mold is electroformed with metal by applying an electroforming solution including the metal ions onto the pre-wetted conductive seed layer. The electroformed metal may then be separated from the polymer mold to form the master pattern.

[0054] The pre-wetting liquid may be a solvent or a mixture of solvents. According to an embodiment, the solvent used to pre-wet the surface has a lower surface tension than the electrolyte solution used in electroforming. Preferably, the pre-wetting solvent is miscible in the electrolyte solution to that it can be displaced in the solution bath. The pre-wetting solution may have a surface tension that is the same or lower than water. The pre-wetting solution may have the same or lower viscosity as water. According to an embodiment, the pre-wetting solvent includes ethanol, isopropyl alcohol, methanol, acetone, water, or a combination of two or more thereof. According to an embodiment, the pre-wetting solvent may optionally include a surfactant. The surfactant may be any suitable surfactant, for example, TRITON X-100, TWEEN, polysorbate, sodium dodecyl sulfate, sodium stearate, or a combination of two or more thereof.

[0055] According to an embodiment, the polymer mold may be made by a casting method. A pre-master may be coated with a release layer. A polymer solution may be cast onto the coated pre-master. The polymer solution may be cured to prepare the polymer mold. The polymer mold may then form the master. Alternatively, the polymer mold may be prepared by embossing the pattern onto a thermoplastic blank.

[0056] In certain embodiments, the pre-master may be a glass master. Any suitable glass may be used for preparing the pre-master. Exemplary glasses that may be used include borosilicate glass, fused silica, soda-lime glass, aluminosilicate glass, or the like. Once the pattern is obtained, the pre-master may be prepared by etching the pattern into the glass master. There are a variety of methods of etching, for example, by ultrashort pulsed lasers, CO2 lasers, CNC machining, chemical wet etching, etc., and combinations of two or more thereof, such as a combination of wet etching and another method (e.g., femtosecond laser followed by wet etching). In certain embodiments, the pattern on the pre-master may be a positive pattern. A positive pattern is the same representation of the original specimen surface contour. In certain embodiments, the pattern on the pre-master may be a negative pattern. A negative pattern is an inverse representation of the original object's surface contour. Once the pre-master is obtained, it may be coated with a release layer. The release layer is configured to help separate the polymer mold from the pre-master in the subsequent process steps. Any suitable materials may be used as a release layer. In certain embodiments, the release layer may be or may include silicone-based materials, parylene, acrylic, wax-based materials, or a fluorochemical coating. After the release layer is applied, the coated pre-master may be secured, for example in a jig, for preparing the polymer mold. A jig may be used to keep polymer mold from bending or moving after it's cured to prevent cracks.

[0057] Any suitable polymer or elastomer may be used for preparing the polymer mold. Exemplary polymers that may be used include polydimethyl siloxane (PDMS), epoxy, polyurethane, polyimide, and novolac resin. In some embodiments, the polymer mold is made by casting a PDMS solution. Suitable PDMS solutions are available, for example, from Dow Chemical under the tradename SYLGARD™, which includes two parts, Part A containing PDMS and Part B containing a curing agent. The parts may be mixed at a suitable ratio, such as 5: 1 to 10: 1 of A:B. In some embodiments the polymer mold is made from a thermoplastic. Thermoplastics are suitable for embossing. Thus, if a thermoplastic is used, the polymer mold may be made by embossing.

[0058] PDMS molding may be done using a variety of methods. The PDMS solution may be cast over the pre-master to make an inverse mold of the master pattern. Typically, a PDMS solution is poured on top of the pre-master and followed by curing. To help the polymer mold preserve the master pattern as completely as possible, mechanical agitation may be used to promote the PDMS solution to fill in features in the pattern. The curing process may include, for example, degassing, thermal aging, UV curing, or a combination thereof.

[0059] To remove the polymer mold from the pre-master, the stack of the polymer mold and the pre-master may be swelled with ethanol to swell the polymer mold slightly. Then the pre-master may be lifted off the polymer mold by a suction cup, leaving the polymer mold in the jig.

[0060] According to an embodiment, the radius of each of the plurality of structures on the polymer mold may be 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less. According to an embodiment, the plurality of structures may be or may include re-entrant structures. The re-reentrant structures may be any suitable re-reentrant structure. FIGS. 2A-2C illustrate examples of various re-entrant structures that may be used in certain embodiments. FIG. 3 illustrates a cross-sectional view of a re-entrant structure on the polymer mold shaped as a hoodoo 500, according to an embodiment, and various dimensions thereof. The hoodoo 500 includes a stem 502 extending from a surface 101, and a cap 504 extending from the stem 502. The cap 504 may include a lip or overhang 524 extending from the perimeter of the cap 504 downward toward the surface 101. The hoodoo 500 defines a longitudinal axis A500. The axis A500 may be perpendicular to the surface 101. The hoodoo 500 may be defined by several parameters including stem height H502, stem radius R502, a, and cap height H504. The cap 504 has a cap radius R504. In certain embodiments, the cap radius R504 may be 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less. The cap radius R504 may have a length in a range of 2 pm to 50 pm, or in certain embodiments 3 pm to 45 pm, or in further embodiments 4 pm to 40 pm, and in further embodiments 5-50 pm. The stem 502 has a radius R502. The radius R502 may have a length in a range of 0.5-100 pm, or in certain embodiments 2-90 pm, or in further embodiments 3-50 pm, and in further embodiments 5-40 pm.

[0061] In some embodiments, the pre-master may have a plurality of inverse hoodoos (or reentrant structures) arranged as a plurality of connected structures to form a continuous hoodoo structure (or continuous re-entrant structure). The plurality of structures may be connected at one or more points. Therefore, the polymer mold (e.g., made from the pre-master) may have a plurality of re-entrant structures. For example, a plurality of hoodoos or re-entrant structures may be attached at the cap or the cap and the stem in a continuous hoodoo structure. An exemplary embodiment of a continuous re-entrant structure is shown in FIG. 4. The continuous re-entrant structure of FIG. 4 may depict the pre-master, the polymer mold, the master pattern (e.g., an intermediate master pattern), or the final article. A plurality of re-entrant structures 600 are attached to each other to form a continuous re-entrant lattice 601 and a plurality of pores 608 dispersed throughout the lattice 601 . The lattice 601 forms an outer surface 605. The lattice 601 is defined by a first lattice pitch Li (center-to-center pore spacing in a first direction). The first lattice pitch Li may be 750 pm or less, 600 pm or less, 500 pm or less, 400 pm or less, 300 pm or less, 200 pm or less, 150 pm or less, 100 pm or less, 65 pm or less, 50 pm or less, or 20 pm or less. The re-entrant structures 600 in a continuous re-entrant lattice 601 may be disposed as an ordered plurality, as shown, or disposed at random. A single continuous re-entrant structure may form a re-entrant layer as discussed above or may be coupled with additional continuous reentrant structures. In some embodiments, the re-entrant structures are arranged such that the spaces between the re-entrant structures form an elongated channel.

[0062] The re-entrant geometry structures 600 of the continuous re-entrant lattice 601 of FIG. 4 include a base 602 (comparable to the stem 502 of the hoodoo 500). The base 602 has a width, W602. The width W602 does not affect breakthrough pressures, but it contributes to the overall permeability of the continuous re-entrant lattice 601 and the permeability of the composite material when the continuous re-entrant lattice 601 is disposed on a porous material. A hoodoo base width W602 may have a range of 0.5 pm to 750 pm, 10 pm to 600 pm, 100 pm to 500 pm, or 250 pm to 500 pm. The width may vary along the length of the stem, and a varying width may provide further advantages in permeability or manufacturing.

[0063] The pores 608 of the continuous lattice structure 601 have a pore diameter D608. The pore diameter D608 is the spacing between the outermost edges of the adjacent re-entrant structures. The pore diameter D608 may be analogous to the edge spacing D530 (space between hoodoos). The pore diameter D608 may be 1 pm or greater, 2 pm or greater, 5 pm or greater, or 10 pm or greater for intended use with low surface tension liquids (e.g., < 30 mN / m). The pore diameter D608 may be 30 pm or less, 20 pm or less, or 10 pm or less for intended use with low surface tension liquids (e.g., < 30 mN / m). The pore diameter D608 may be in a range of 1 pm to 30 pm for intended use with low surface tension liquids (e.g., < 30 mN / m). The pore diameter D608 may be 10 pm or greater, 30 pm or greater, 50 pm or greater, or 100 pm or greater and up to 2 mm for intended use with high surface tension liquids (e.g., > 30 mN / m).

[0064] In addition, the hoodoos or re-entrant structures that make up the continuous hoodoo or re-entrant structure (lattice) share many of the same dimensions as the discrete hoodoos or reentrant structures discussed above in connection with an ordered plurality of hoodoos. For example, the stem height H602 of each structure may be 0 pm or greater, 2 pm or greater, 5 pm or greater, or 10 pm or greater. The stem height H602 be 100 pm or less, 65 pm or less, 50 pm or less, or 20 pm or less. The stem height H602 may range from 0 pm to 65 pm, from 2 pm to 65 pm, from 2 pm to 20 pm, or from 10 pm to 50 pm. In a continuous hoodoo or re-entrant structure (lattice), the stem heights are substantially uniform across the continuous structure as the hoodoos are attached together to form a substantially flat outer surface 605. Herein, “substantially flat” refers to a surface that is planar but may deviate within manufacturing tolerances. Even though the hoodoo structures are attached at the caps, the cap height H604 may still be measured from the upper / outer surface of the cap to the outer radius. The height H604 of the cap 604 may be 0 pm or greater and 3 pm or less, 5 pm or less, or 10 pm or less. The height H504 may range from 0 pm to 10 pm, from 0 pm to 5 pm, or from 0 pm to 3 pm.

[0065] In order to make through-holes in an article (such as the continuous re-entrant structures shown in FIG. 4) being formed by the master pattern, the master pattern may include structures with a long pin that is capable of puncturing through a polymer film. An example of such structure 700 is shown in FIG. 5A. The structure 700 includes a base 704 and a pin 702 extending from the base 704. The base 704 may be seated on a surface 701. The pin 702 has a height H702 and a width W702. The height H702 and width W702 have an aspect ratio H: W. The aspect ratio H:W may be 1: 1 or greater, 1.3:1 or greater, 1.5:1 or greater, 2: 1 or greater, 2.5:1 or greater, 3 : 1 or greater, or 3.5 : 1 or greater.

[0066] The master pattern with structures 700 of FIG. 5 A may be made using a mold or intermediate master with an inverse structure 800 shown in FIG. 5B. The inverse structure 800 includes a base cavity 804 and a pin cavity 802 extending from the base cavity 804. The pin cavity 802 has a height H802 and width W802 that correspond to the height H702 and width W702 of the structure 700. The height H802 and width W802 have an aspect ratio H:W. The aspect ratio H:W may be 1 :1 or greater, 1.3: 1 or greater, 1.5:1 or greater, 2:1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater.

[0067] The present disclosure provides methods of forming a master pattern from a mold including structures with a radius of 100 pm or less. The structure having this small radius (100 pm or less) may be the structure as a whole (thus, referring to the radius or half-width of the base 704 or base cavity 804 in FIGS. 5A and 5B), or a portion of the structure, such as the pin in FIGS. 5A and 5B (thus, referring to the radius of half-width of the pin 702 or pin cavity 802 in FIGS. 5A and 5B). The methods of the present disclosure may be particularly useful for preparing master patterns from a mold including structures with small radius (e.g., 100 pm or less) and a high aspect ratio (e.g., 1: 1 or greater, 1.3: 1 or greater, 1.5: 1 or greater, 2:1 or greater, 2.5:1 or greater, 3: 1 or greater, or 3.5: 1 or greater). According to an embodiment, the mold is pre-wetted prior to electroforming the master pattern. If an intermediate master pattern is formed, the intermediate master pattern may be prewetted prior to electroforming the master pattern. In some embodiments, both the mold and the intermediate master pattern are pre- wetted prior to electroforming. In some embodiments, only the part that includes a pin cavity with an aspect ratio of 1 : 1 or greater, 1.3: 1 or greater, 1.5:1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3 : 1 or greater, or 3.5 : 1 or greater, is pre-wetted prior to electroforming. This may be either the mold or the intermediate master pattern.

[0068] Once the polymer mold is obtained, it may be coated with a conductive seed layer. A conductive seed layer may be applied onto the polymer mold prior to electroforming. The conductive seed layer is used to help a voltage to be applied on the polymer mold in order to perform the electroforming. Any suitable method may be used to apply the conductive seed layer onto the polymer mold. In certain embodiments, the conductive seed layer may be applied onto the polymer mold by sputter coating. Any suitable materials may be used as a conductive seed layer. The conductive seed layer may be or may include gold, chromium, nickel, sliver. The conductive seed layer may be or may include any suitable material that is applied in a way that helps ensure good adhesion to the polymer mold. The suitable material may help the conductive seed layer to be applied in a conformal manner, for example, a “wrinkling” of the seed layer is minimized. Once the polymer mold coated with the conductive seed layer is obtained, the conductive seed layer may be pre-wetted with a solvent prior to electroforming. Pre-wetting the polymer mold coated with the conductive seed layer may help to preserve the small features from the polymer mold in the master pattern, specifically smaller holes or pins. The pre-wetting may be or may include any suitable methods, for example, dipping, immersing, pouring, adding dropwise, spraying, brushing, flooding, or the like. According to an embodiment, the solvent used to pre-wet the conductive seed layer may include ethanol, isopropyl alcohol, methanol, acetone, water, or a combination of two or more thereof.

[0069] The electroforming solution may be applied by submerging the pre-wetted polymer mold into the electroforming solution. In certain embodiments, the electroforming solution may include or may be a metal, for example, nickel, copper, silver, gold, brass, titanium, iron, chromium, or a combination of two or more thereof. After the electroforming process is accomplished, the electroformed metal may then be separated from the polymer mold to form the master pattern.

[0070] To separate the master pattern from the polymer mold, it may be optionally swell the electroformed polymer mold with ethanol to swell the polymer mold slightly and then separate the master pattern from the polymer mold. In certain embodiments, the master pattern or an inverted master pattern may be formed by the electroformed metal. In some embodiments, the master pattern is a first master, and a second metal master may be made from the first metal master. In such cases, the first master may be referred to as an intermediate master. In certain embodiments, the master pattern may have a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

[0071] According to an embodiment, a master pattern made by a method includes forming a polymer mold and electroforming a metal onto the mold as described above. The term electroforming is used here broadly and encompasses electroplating. According to an embodiment, a method of making a master pattern includes forming a polymer mold and electroforming a metal onto the mold. The polymer mold may have a pattern with a plurality of structures. The method includes applying a conductive seed layer onto the polymer mold. The method may further include pre-wetting the conductive seed layer with a solvent prior to electroforming. Pre-wetting of the conductive seed layer may help the electroforming solution to reach all the contours of the pattern. In particular, when the mold includes a cavity with a high aspect ratio (e.g., a pin hole with an aspect ratio of 1 : 1 or greater, 1.3:1 or greater, 1.5: 1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3 : 1 or greater, or 3.5:1 or greater), pre-wetting may be helpful to reduce or avoid defects. After pre-wetting, the polymer mold is electroformed with a metal by applying an electroforming solution including the metal ions onto the pre-wetted conductive seed layer. The electroformed metal may then be separated from the polymer mold to form the master pattern. The master pattern may have a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master. In some embodiments, the master pattern is an intermediate master, and a second master pattern may be made by electroforming a metal onto the intermediate master. The first master may be pre-wetted prior to electroforming. The second master may be made by applying an electroforming solution including the metal ions onto the intermediate master. The electroformed metal may then be separated from the first master to form the second master pattern. In some embodiments, it may be desirable to provide a continuous re-entrant structure (lattice) with drains. In practice, when a continuous re-entrant structure (lattice) is applied onto a relatively large surface area. The continuous re-entrant structure (lattice) may be provided with drains or exit structures to allow any possible breakthrough liquid to escape rather than to penetrate adjacent pores. The term breakthrough liquid is used here to refer to a liquid that has broken through the repellent barrier provided by the re-entrant structures. Breakthrough liquid may have come into contact with the substrate surface. One example of drains and exit structures to direct breakthrough liquid in a polymer mold are shown in FIGS. 6A to 6B.

[0072] The bottom plan view of a polymer mold with a continuous lattice with re-entrant hoodoo structures and drainage channels is shown in FIG. 6A. FIG. 6B is a cross-sectional side view of the continuous lattice of FIG. 6A. The continuous re-entrant structure (lattice) 1630 includes a plurality of re-entrant structures 1600 connected to one another, and a plurality of pores 1608 formed between the plurality of re-entrant structures 1600. The re-entrant structures 1600 include caps 1604, which form the outer surface 1605 of the lattice. The re-entrant structures 1600 include stems 1602 that define a bottom surface 1606 of the lattice. In some instances, liquid may break through and enter one of the pores 1608. The bottom surface 1606 may include one or more grooves or drains 1610. Any liquid that enters the pore 1608 may flow into the drain 1610. The drain 1610 may be sized so that the liquid can flow away from the pore via capillary action.

[0073] The drains may be configured in any suitable way and may include different geometries and pore groupings. While many possible configurations and shapes may be used, structures that utilize hexagons or a honey-comb like structure may be more closely packed and result in a more efficient lattice structure. The pores may be grouped within the drain geometries in various ways. The number of pores within a drainage structure may be determined based, among other things, on desired efficiency of drainage (fewer pores per drainage structure results in more efficient drainage), the impact on structural integrity (drainage structures spaced further apart result in better structural integrity), and the estimated need for drainage (an estimated population density of breakthrough structures). In some embodiments, the number of pores per drainage structure (one continuous drain loop) is 1 or greater and up to 50, up to 25, up to 10, up to 7, or up to 4. In some embodiments, each pore of the lattice is adjacent to a drain. A lattice may include drainage structures of different shapes and sizes. In some embodiments, various tessellating patterns of drainage structures may be used to adjust the group size. In some embodiments, the drainage structures form channels that extend the entire width of the substrate. In other embodiments, the channels only extend part of the width of the substrate.

[0074] Illustrative Embodiments

[0075] The technology described herein is defined in the claims. However, below is provided a non-exhaustive listing of non-limiting embodiments. Any one or more of the features of these embodiments may be combined with any one or more features of another example, embodiment, or aspect described herein.

[0076] Embodiment l is a method of making a master pattern, the method comprising: forming a polymer mold comprising a pattern with a plurality of structures, each of the structures having a radius of 100 pm or less; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising the metal ions onto the pre-wetted conductive seed layer; and separating the electroformed metal from the polymer mold to form the master pattern.

[0077] Embodiment 2 is the method of embodiment 1, wherein the forming of the polymer mold comprises: coating a pre-master with a release layer; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare the polymer mold; and separating the polymer mold from the pre-master.

[0078] Embodiment 3 is the method of embodiment 1 or 2, wherein the forming of the polymer mold comprises embossing the pattern onto a thermoplastic blank. Embodiment 4 is the method of any one of embodiments 1 to 3, wherein the radius of each of the plurality of structures is 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less.

[0079] Embodiment 5 is the method of any one of embodiments 1 to 4, wherein the radius of each of the plurality of structures is from 0.1 pm to 50 pm, from 1 pm to 30 pm, from 2 pm to 20 pm, or from 5 pm to 10 pm.

[0080] Embodiment 6 is the method of any one of embodiments 1 to 5, wherein the plurality of structures have an aspect ratio (height to width) of 1 : 1 or greater, 1.3: 1 or greater, 1.5:1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater.

[0081] Embodiment 7 is the method of any one of embodiments 1 to 6, wherein the plurality of structures have an aspect ratio (height to width) of 10:1 or less.

[0082] Embodiment 8 is the method of any one of embodiments 1 to 7, wherein the plurality of structures comprises re-entrant structures.

[0083] Embodiment 9 is the method of any one of embodiments 1 to 8, wherein the master pattern comprises a plurality of pins corresponding to the plurality structures of the polymer mold.

[0084] Embodiment 10 is the method of embodiment 9, wherein the plurality of pins have a radius of 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less.

[0085] Embodiment 11 is the method of embodiment 9, wherein the plurality of pins have a radius from 0.1 pm to 50 pm, from 1 pm to 30 pm, from 2 pm to 20 pm, or from 5 pm to 10 pm.

[0086] Embodiment 12 is the method of any one of embodiments 9 to 11, wherein the plurality of pins have an aspect ratio (height to width) of 1 : 1 or greater, 1.3: 1 or greater, 1.5: 1 or greater, 2: 1 or greater, 2.5:1 or greater, 3:1 or greater, or 3.5: 1 or greater.

[0087] Embodiment 13 is the method of any one of embodiments 9 to 12, wherein the plurality of pins have an aspect ratio (height to width) of 10: 1 or less.

[0088] Embodiment 14 is the method of any one of embodiments 2 to 13, wherein the pre-master is a glass master. Embodiment 15 is the method of embodiment 14, wherein the pre-master is prepared by etching the pattern into the glass master.

[0089] Embodiment 16 is the method of embodiment 15, wherein the etching is done using a femtosecond laser.

[0090] Embodiment 17 is the method of any one of embodiments 1 to 16, wherein the pattern is a positive pattern.

[0091] Embodiment 18 is the method of any one of embodiments 1 to 17, wherein the pattern is a negative pattern.

[0092] Embodiment 19 is the method of any one of embodiments 1 to 18, wherein the release layer comprises fluorosilane.

[0093] Embodiment 20 is the method of any one of embodiments 1 to 19, wherein the conductive seed layer is applied onto the polymer mold by sputter coating.

[0094] Embodiment 21 is the method of any one of embodiments 1 to 20, wherein the solvent comprises ethanol, isopropyl alcohol, methanol, acetone, water, or a combination of two or more thereof.

[0095] Embodiment 22 is the method of any one of embodiments 1 to 21, wherein the electroforming solution is applied by submerging the polymer mold into the electroforming solution.

[0096] Embodiment 23 is the method of any one of embodiments 1 to 22, wherein the metal is selected from nickel, copper, silver, gold, brass, titanium, iron, chromium, or a combination of two or more thereof.

[0097] Embodiment 24 is the method of any one of embodiments 1 to 23, wherein the electroformed metal forms the master pattern.

[0098] Embodiment 25 is the method of any one of embodiments 1 to 24, wherein the electroformed metal forms an inverted master pattern.

[0099] Embodiment 26 is the method of any one of embodiments 2 to 25, wherein the master pattern comprises a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master. Embodiment 27 is a master pattern made by a method comprising: coating a pre-master with a release layer, the pre-master comprising a pattern comprising a plurality of structures having a radius of 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare a polymer mold; separating the polymer mold from the pre-master; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising metal ions onto the pre-wetted conductive seed layer; and separating the electroformed metal from the polymer mold to form the master pattern, wherein the master pattern exhibits at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

[0100] Embodiment 28 is the master pattern of embodiment 27, wherein the radius of each of the plurality of structures is from 0.1 pm to 50 pm, from 1 pm to 30 pm, from 2 pm to 20 pm, or from 5 pm to 10 pm.

[0101] Embodiment 29 is the master pattern of embodiment 27 or 28, wherein the plurality of structures have an aspect ratio (height to width) of 1 : 1 or greater, 1.3: 1 or greater, 1.5: 1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5:1 or greater.

[0102] Embodiment 30 is the master pattern of any one of embodiments 27 to 29, wherein the plurality of structures have an aspect ratio (height to width) of 10: 1 or less.

[0103] Embodiment 31 is the master pattern of any one of embodiments 27 to 30, wherein the plurality of structures comprises re-entrant structures.

[0104] Embodiment 32 is the master pattern of any one of embodiments 27 to 31, wherein the master pattern comprises a plurality of pins corresponding to the plurality structures of the polymer mold. Embodiment 33 is the master pattern of embodiment 32, wherein the plurality of pins have a radius of 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less.

[0105] Embodiment 34 is the master pattern of embodiment 32 or 33, wherein the plurality of pins have a radius from 0.1 pm to 50 pm, from 1 pm to 30 pm, from 2 pm to 20 pm, or from 5 pm to 10 pm.

[0106] Embodiment 35 is the master pattern of any one of embodiments 32 to 34, wherein the plurality of pins have an aspect ratio (height to width) of 1 : 1 or greater, 1.3: 1 or greater, 1.5: 1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater.

[0107] Embodiment 36 is the master pattern of any one of embodiments 32 to 35, wherein the plurality of pins have an aspect ratio (height to width) of 10: 1 or less.

[0108] Embodiment 37 is the master pattern of any one of embodiments 27 to 36, wherein the pre-master is a glass master.

[0109] Embodiment 38 is the master pattern of embodiment 37, wherein the pre-master is prepared by etching the pattern into the glass master.

[0110] Embodiment 39 is the master pattern of embodiment 38, wherein the etching is done using a femtosecond laser.

[0111] Embodiment 40 is the master pattern of any one of embodiments 27 to 39, wherein the pattern is a positive pattern.

[0112] Embodiment 41 is the master pattern of any one of embodiments 27 to 40, wherein the pattern is a negative pattern.

[0113] Embodiment 42 is the master pattern of any one of embodiments 27 to 41, wherein the release layer comprises fluorosilane.

[0114] Embodiment 43 is the master pattern of any one of embodiments 27 to 42, wherein the conductive seed layer is applied onto the polymer mold by sputter coating.

[0115] Embodiment 44 is the master pattern of any one of embodiments 27 to 43, wherein the solvent comprises ethanol, isopropyl alcohol, methanol, acetone, water, or a combination of two or more thereof. Embodiment 45 is the master pattern of any one of embodiments 27 to 44, wherein the electroforming solution is applied by submerging the polymer mold into the electroforming solution.

[0116] Embodiment 46 is the master pattern of any one of embodiments 27 to 45, wherein the metal is selected from nickel, copper, silver, gold, brass, titanium, iron, chromium, or a combination of two or more thereof

[0117] Embodiment 47 is the master pattern of any one of embodiments 27 to 46, wherein the electroformed metal forms the master pattern.

[0118] Embodiment 48 is the master pattern of any one of embodiments 27 to 47, wherein the electroformed metal forms an inverted master pattern.

[0119] Embodiment 49 is the master pattern of any one of embodiments 27 to 48, wherein the master pattern exhibits at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

[0120] Examples

[0121] A master pattern with re-entrant structures was replicated at a microscale. The master pattern was designed to repel liquids with low surface tensions (> 20 mN / m) without the use of any chemical coating. The master pattern with re-entrant structures were made through the method described above. FIG. 7A is a schematic cross-sectional side view of an article with a hoodoo re-entrant structure. The article depicted in FIG. 7A may be the polymer mold used to prepare the master pattern. The article depicted in FIG. 7A may be the final re-entrant structure made using the master pattern. The re-entrant structures on the polymer mold may be made by any of the methods discussed herein. According to an embodiment, the re-entrant geometries include a plurality of structures having a radius of 100 pm or smaller. Preparing master patterns for articles with such microscale re-entrant geometries using conventional methods has proved to be challenging.

[0122] FIGS. 7B and 7C are SEM images of master patterns with and without pre-wetting prior to electroforming. FIG. 7B is a microscopic image of a master pattern with pre-wetting prior to electroforming. FIG. 7C is a microscopic image of a master pattern without pre-wetting prior to electroforming. The master pattern with pre-wetting prior to electroforming has a relatively smooth surface as shown in FIG. 7B. The master pattern without pre-wetting prior to electroforming has a relatively uneven surface with dents as shown in FIG. 7C. Furthermore, the master pattern without pre-wetting prior to electroforming has defective features, such as missing a pin structure and having a hollow center pin instead. The master pattern with pre-wetting prior to electroforming as shown in FIG. 7B. The pre-wetting has preserved more features from the pre-master when compared with the master pattern without pre-wetting prior to electroforming as shown in FIG. 7C. In addition to fewer deformities, the structure made with pre-wetting includes a complete pin structure. All references and publications cited herein are expressly incorporated herein by reference in their entirety into this disclosure, except to the extent they may directly contradict this disclosure. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. It should be understood that this disclosure is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the disclosure intended to be limited only by the claims set forth here.

Claims

CLAIMS1. A method of making a master pattern, the method comprising: forming a polymer mold comprising a pattern with a plurality of structures, each of the structures having a radius of 100 pm or less; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising metal ions onto the pre-wetted conductive seed layer; and separating the electroformed metal from the polymer mold to form the master pattern.

2. The method of claim 1, wherein the forming of the polymer mold comprises: coating a pre-master with a release layer; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare the polymer mold; and separating the polymer mold from the pre-master.

3. The method of claim 1 or 2, wherein the forming of the polymer mold comprises embossing the pattern onto a thermoplastic blank.

4. The method of any one of claims 1 to 3, wherein the radius of each of the plurality of structures is 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less.

5. The method of any one of claims 1 to 4, wherein the plurality of structures have an aspect ratio (height to width) of 1 : 1 or greater, 1.3: 1 or greater, 1.5:1 or greater, 2: 1 or greater, 2.5: 1 or greater, 3: 1 or greater, or 3.5: 1 or greater.

6. The method of any one of claims 1 to 5, wherein the plurality of structures comprises reentrant structures.

7. The method of any one of claims 2 to 6, wherein the pre-master is a glass master.

8. The method of claim 7, wherein the pre-master is prepared by etching the pattern into the glass master.

9. The method of claim 8, wherein the etching is done using a femtosecond laser.

10. The method of any one of claims 1 to 9, wherein the pattern is a positive pattern.

11. The method of any one of claims 1 to 10, wherein the pattern is a negative pattern.

12. The method of any one of claims 2 to 11, wherein the release layer comprises fluorosilane.

13. The method of any one of claims 1 to 12, wherein the conductive seed layer is applied onto the polymer mold by sputter coating.

14. The method of any one of claims 1 to 13, wherein the solvent comprises ethanol, isopropyl alcohol, methanol, acetone, water, or a combination of two or more thereof.

15. The method of any one of claims 1 to 14, wherein the electroforming solution is applied by submerging the polymer mold into the electroforming solution.

16. The method of any one of claims 1 to 15, wherein the metal is selected from nickel, copper, silver, gold, brass, titanium, iron, chromium, or a combination of two or more thereof.

17. The method of any one of claims 1 to 16, wherein the electroformed metal forms the master pattern.

18. The method of any one of claims 1 to 17, wherein the electroformed metal forms an inverted master pattern.

19. The method of any one of claims 2 to 18, wherein the master pattern comprises a at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

20. A master pattern made by a method comprising:coating a pre-master with a release layer, the pre-master comprising a pattern comprising a plurality of structures having a radius of 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, or 10 pm or less; casting a polymer solution onto the coated pre-master; curing the polymer solution to prepare a polymer mold; separating the polymer mold from the pre-master; applying a conductive seed layer comprising gold onto the polymer mold; pre-wetting the conductive seed layer with a solvent; electroforming the polymer mold with a metal by applying an electroforming solution comprising metal ions onto the pre-wetted conductive seed layer; and separating the electroformed metal from the polymer mold to form the master pattern, wherein the master pattern exhibits at least 90 %, at least 95 %, at least 98 %, or at least 99 % replication of the pattern of the pre-master.

Images