Methods for forming superhydrophobic coatings, articles comprising superhydrophobic coatings, and additive manufacturing systems for superhydrophobic coatings

Abstract

Methods for forming superhydrophobic coatings, articles including superhydrophobic coatings, and additive manufacturing systems for superhydrophobic coatings are provided. The method includes aerosolizing a solution includes a polymer and a solvent, thereby producing a mist including droplets of the solution entrained in a gas. The method includes directing the mist to a substrate. The mist traverses to the substrate over a flight time. The method includes decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles. The method includes contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate. The superhydrophobic coating includes the gel particles.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICEPCT APPLICATION FOR METHODS FOR FORMING SUPERHYDROPHOBIC COATINGS, ARTICLES COMPRISING SUPERHYDROPHOBIC COATINGS, AND ADDITIVE MANUFACTURING SYSTEMS FOR SUPERHYDROPHOBIC COATINGSInventors: Ke Zhong, Jace Rozsa, Mohammad F. Islam, Gary K. Fedder, Dinesh K. Patel, and Lining YaoRELATED APPLICATIONS

[0001] The present application claims priority to United States provisional patent application Serial No. 63 / 636,221, filed April 19, 2024, which is incorporated herein by reference in its entirety.GOVERNMENT RIGHTS

[0002] This invention was made with United States government support under 2047912 awarded by the National Science Foundation (NSF). The U. S. government has certain rights in the invention.BACKGROUND

[0003] Nature abounds with self-cleaning or superhydrophobic surfaces that support diverse lifeforms. For example, the superhydrophobicity of lotus leaves, attributed to their micrometer- and nanometer-scale surface features, can enable water droplets to roll off, effectively cleaning the leaves by removing dirt particles. Similarly, desert beetles possess superhydrophobic surfaces to harvest water from fog, while the scales on shark skin confer superhydrophobicity to reduce drag. These natural phenomena have inspired scientists and engineers to create superhydrophobic surfaces for diverse applications. There are challenges with creating superhydrophobic surfaces.SUMMARY

[0004] According to general aspects, the present disclosure provides a method for forming a superhydrophobic coating. The method comprises aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas. The method comprises directing the mist to a substrate. The mist traverses to the substrate over a flight time. The method comprises decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles. In variousexamples, decreasing a dampening factor of the droplets comprises removing at least a portion of the solvent from the droplets by evaporation during the flight time to increase a concentration of the polymer within the droplets and / or polymerizing the polymer. The method comprises contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate. The superhydrophobic coating comprises the gel particles.

[0005] In other general aspects, the present disclosure provides an article produced by the method for forming a superhydrophobic coating.

[0006] In yet other general aspects, the present disclosure provides an additive manufacturing system configured to perform the method for forming a superhydrophobic coating.

[0007] Various embodiments and implementations of the present invention provide many benefits and improvements relative to prior coating techniques. For example, the methods according to the present disclosure can be straightforward to fabricate superhydrophobic surfaces using a marginally hydrophobic polymer and can enhance efficiency of the technique, printability, control of hydrophobicity, and / or control of the structure of the superhydrophobic surface. The methods according to the present disclosure can enhance spatial control of forming superhydrophobic coating, such as, for example, forming patterns of superhydrophobic regions in a plane of a substrate, forming varying height superhydrophobic surfaces (e.g., forming hillocks and ridges), and / or forming gradients of hydrophobicity to superhydrophobicity. These and other benefits that are potentially realizable through various implementations of the present invention will be apparent from the description that follows.

[0008] It will be understood that the invention disclosed and described in this specification is not limited to the aspects summarized in this Summary. The reader will appreciate the foregoing details, as well as others, upon considering the following detailed description of various non-limiting and non-exhaustive aspects according to this specification.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features and advantages of the examples presented herein, and the manner of attaining them, will become more apparent, and the examples will be better understood, by reference to the following description taken in conjunction with the accompanying drawings, wherein:

[0010] FIG. 1 is a schematic diagram illustrating fabrication of superhydrophobic surfaces according to the present disclosure, and showing the contrast of fabrication with solvent at two different vapor pressures as examples.

[0011] FIG. 2A is an image of as-prepared solutions comprising polymer and solvent (tetrahydrofuran (THF), dimethylformamide (DMF), and N-Methyl-2-pyrrolidone (NMP)) in vials in a liquid state, indicating that the solutions flow under gravity when the vials are inverted with vial caps down.

[0012] FIG. 2B is an image of the solutions of FIG. 2A after sufficient evaporation to transition the solutions to a gel state where the gelled polymer solutions do not flow under gravity when the vials are inverted.

[0013] FIG. 3 A is a schematic diagram of the ultrasonic aerosolization of DS-PDMS solutions on the left and subsequent deposition of generated droplets on a substrate using aerosol jetting printing on the right. The zoom-in schematic on the left shows the DS-PDMS network, consisting of PDMS polymer chains (lines) and disulfide bonds (dots). The schematic diagram on the right provides a sectional view of the printer’s deposition head.

[0014] FIG. 3B is a graph illustrating the calculated <bDS. PDMSas a function of time plotted for the solvent THF at an initial volume fraction ^DS-POMS=^.041± 0.002. The labels represent different initial droplet radii. The curves represent the evolution of droplet radii with time and hence <bDS. PDMSfor droplets with different initial radii. The vertical dashed line identifies flight time (Zflight) and the horizontal dotted line represents 4*f^s-PDMS• ^DS-PDMSdroplets with initial radii labeled to the left of the vertical dashed line would reachprior to time equaling the tfiight.

[0015] FIG. 3C is a graph illustrating the calculated <bDS. PDMSas a function of time plotted for the solvent DMF at an initial volume fraction ^DS-POMS=^ 041± 0.002. The labels represent different initial droplet radii. The curves represent the evolution of droplet radii with time and hence <bDS. PDMSfor droplets with different initial radii. The vertical dashed line identifies ^flightand the horizontal dotted line represents 4*|)es_PDMS- ^DS-PDMS ’Ndroplets with initial radii labeled to the left of the vertical dashed line would reach d)®e'

[0016] FIG. 3D is a graph illustrating the calculated <bDS. PDMSas a function of time plotted for the solvent NMP at an initial volume fraction=0.041± 0.002. The labels represent different initial droplet radii. The curves represent the evolution of droplet radiiwith time and hence <DS. PDMSfor droplets with different initial radii. The vertical dashed line identifies Zflightand the horizontal dotted line represents 4*f^s_PDMS- ^DS-PDMS ’Ndroplets with initial radii labeled to the left of the vertical dashed line would reach d)®e'Dn, „.

[0017] FIG. 4A is scanning electron microscope (SEM) images of Aerosol Jet (AJ)-printed surfaces with DS-PDMS solutions using THF showing surface morphology. The top right inset image is a high-resolution SEM image to capture the microstructure of the printed surface and the bottom right inset optical image shows the shape of a water droplet on the printed surface to reflect the hydrophobicity for contact angle (CA) measurements.

[0018] FIG. 4B is SEM images of AJ-printed surfaces with DS-PDMS solutions using DMF showing surface morphology. The top right inset image is a high-resolution SEM image to capture the microstructure of the printed surface and the bottom right inset optical image shows the shape of a water droplet on the printed surface to reflect the hydrophobicity for CA measurements.

[0019] FIG. 4C is SEM images of AJ-printed surfaces with DS-PDMS solutions using NMP showing surface morphology. The top right inset image is a high-resolution SEM image to capture the microstructure of the printed surface and the bottom right inset optical image is the shape of a water droplet on the printed surface to reflect the hydrophobicity for CA measurements.

[0020] FIG. 4D is SEM images of AJ-printed surfaces with DS-PDMS solutions using THF showing surface morphology. The top right inset image is a high-resolution SEM image to capture the microstructure of the printed surface and the bottom right inset optical image is the shape of a water droplet on the printed surface to reflect the hydrophobicity for CA measurements.

[0021] FIG. 4E is a chart illustrating distributions of droplet radii for surfaces fabricated using DS-PDMS solutions

[0022] FIG. 4F is a chart illustrating distributions of droplet radii for surfaces with (DS-

[0023] FIG. 5A is SEM images of AJ-printed surfaces using (DS-PDMS, THF) after heating illustrating that the surface has become smooth with a measured CA at 99° ± 2°. The top left inset optical image shows the shape of a water droplet on the printed surface to reflect the hydrophobicity for CA measurements. The top right inset image is a higher magnification SEM image.

[0024] FIG. 5B is SEM images of AJ-printed surfaces using (DS-PDMS, DMF) after heating illustrating that the surface has become smooth with a measured CA at 98° ± 2°. The top left inset optical image shows the shape of a water droplet on the printed surface to reflect the hydrophobicity for CA measurements.

[0025] FIG. 5C is a chart illustrating a comparison of CAs before and after heating surfaces fabricated with polymer solutions using three different solvents (THF, DMF, and NMP). All surfaces show very similar CAs after heating, comparable to the CA of intrinsic DS-PDMS.

[0026] FIG. 6A is optical images illustrating two parallel meandering superhydrophobic lines formed according to an example to create a hydrophilic silicon channel to guide and move a water droplet along the channel when the substrate is tilted. Scale bar is 5 mm.

[0027] FIG. 6B is images illustrating two parallel arc-shaped lines formed according to an example to create a channel that guides two droplets to move to the center reservoir for mixing by tilting the substrate. Scale bar is 5 mm.

[0028] FIG. 6C is optical images illustrating a water droplet moving from the right narrower side to the left wider side of a tapered channel without tilting the substrate. Scale bar is 5 mm.

[0029] FIG. 6D is optical images illustrating oil separating from water when a water-oil mixture is placed on the superhydrophobic surface. Scale bar is 5 mm.

[0030] FIG. 6E is optical images illustrating an approximately 1 mm diameter well that entrains a water droplet and impedes its evaporation compared to droplets placed on the adjacent bare silicon surface. A 5 pL water droplet on silicon evaporated within 27 min and the same size droplet on the printed microarray evaporated within 44 min. Scale bar is 1 mm.

[0031] FIG. 7 is a schematic of a chemical synthesis for disulfide-polydimethylsiloxane (DS-PDMS).

[0032] FIG. 8 is a flow chart illustrating a method of forming a superhydrophobic surface according to the present disclosure.

[0033] FIG. 9 is an article comprising a superhydrophobic surface according to the present disclosure.

[0034] FIG. 10 is an additive manufacturing system for forming a superhydrophobic surface according to the present disclosure.

[0035] FIG. 11 is SEM images illustrating a surface fabricated by drop casting 5 pL of polymer solution with ^(DS-PDMS THF)=0041 ± 0.002 on a polytetrafluoroethylene substrate. The polymer solution includes DS-PDMS and NMP. The top left inset optical image showsthe shape of a water droplet on the surface to reflect the hydrophobicity for CA measurements. The measured CA is 99° ± 1°. The top right inset image is a higher magnification image, revealing a smooth surface with no observable features.

[0036] FIG. 12A is SEM images of AJ-printed surfaces with (DS-PDMS, DMF) solutions at ^(DS-PDMS DMF)=^ 041 ± 0.002 using a 150 pm diameter nozzle, showing spherical droplets deposited on a smooth surface at first magnification.

[0037] FIG. 12B is SEM images of AJ-printed surfaces with (DS-PDMS, DMF) solutions at ^(DS-PDMS DMF)=^ 041 ± 0.002 using a 150 pm diameter nozzle, showing spherical droplets deposited on a smooth surface at a higher magnification.

[0038] FIG. 12C is an optical image showing the shape of a water droplet on the surface to reflect the hydrophobicity for CA measurements. The measured CA is 113° ± 1°.

[0039] FIG. 12D is SEM images of AJ-printed surfaces with (DS-PDMS, DMF) solutions at ^(DS-PDMS DMF)=^ 041 ± 0.002 using a 300 pm diameter nozzle, showing a lower number density of deposited droplets due to the larger line width at first magnification.

[0040] FIG. 12E is SEM images of AJ-printed surfaces with (DS-PDMS, DMF) solutions at ^(DS-PDMS DMF)=^ 041 ± 0.002 using a 300 pm diameter nozzle, showing a lower number density of deposited droplets due to the larger line width a higher magnification.

[0041] FIG. 12F is an image showing the shape of a water droplet on the surface to reflect the hydrophobicity for CA measurements. The measured CA is 98° ± 1°.

[0042] FIG. 13 is SEM images of AJ-printed surfaces with (DS-PDMS, NMP) solutions at ^(DS-PDMS NMP)=0041 ± 0.002 after heating to90 °C. The top left inset optical image shows the shape of a water droplet on the surface to reflect the hydrophobicity for CA measurements. The measured CA is 97° ± 2°. The top right inset image is a higher magnification image, showing a smooth surface after heating.

[0043] FIG. 14A are optical microscopic images of an S-shaped channel for droplet manipulation.

[0044] FIG. 14B are optical microscopic images of an arc-shaped channel guiding two droplets for mixing as a microscale reactor.

[0045] FIG. 14C are optical microscopic images of a tapered channel for droplet manipulation without tilting the surface.

[0046] FIG. 14D are optical microscopic images of a microarray serving as wells for water droplet retention. The bottom image shows a 1 mm diameter well with the exposed baresilicon center, where the dark horizontal lines are the printing paths and the particles near the well are overspray.

[0047] FIG. 15A is an SEM image of the cross-section of AJ-printed superhydrophobic surfaces created with (DS-PDMS, THF) solutions at a low magnification.

[0048] FIG. 15B is an SEM image of the cross-section of AJ-printed superhydrophobic surfaces created with (DS-PDMS, THF) solutions at a moderate magnification.

[0049] FIG. 15C is an SEM image of the cross-section of AJ-printed superhydrophobic surfaces created with (DS-PDMS, THF) solutions at a high magnification.

[0050] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate certain embodiments, in one form, and such exemplifications are not to be construed as limiting the scope of the appended claims in any manner.DETAILED DESCRIPTION

[0051] Various examples are described and illustrated herein to provide an overall understanding of the structure, function, and use of the disclosed methods, superhydrophobic coatings, and systems. The various examples described and illustrated herein are nonlimiting and non-exhaustive. Thus, the invention is not limited by the description of the various non-limiting and non-exhaustive examples disclosed herein. Rather, the invention is defined solely by the claims. The features and characteristics illustrated and / or described in connection with various examples may be combined with the features and characteristics of other examples. Such modifications and variations are intended to be included within the scope of this specification. As such, the claims may be amended to recite any features or characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Further, Applicant reserves the right to amend the claims to affirmatively disclaim features or characteristics that may be present in the prior art. The various examples disclosed and described in this specification can comprise, consist of, or consist essentially of the features and characteristics as variously described herein.

[0052] One approach to achieving superhydrophobicity is by selecting materials with chemical structures and intermolecular forces that can result in very low surface energy, thereby creating extremely poor wetting properties. However, the present inventors determined there are challenges in designing materials with tunable intermolecular interactions.

[0053] Manipulating surface morphology to include multiscale roughness, which traps air and reduces the surface contact area for water, can enhance hydrophobicity. Conventionalfabrication processes such as vapor deposition, hydrothermal synthesis, electrochemical deposition, lithography, and sol-gel processing can be used to create superhydrophobic surfaces with micrometer- or nanometer-scale features. These techniques often require complex and stringent experimental conditions and multistep processing, limiting their scalability and applicability. The present inventors determined that more straightforward and scalable fabrication methods like spray coating, dip coating, and electrospinning have not gained wide usage for superhydrophobic surface manufacturing due to limited control over surface roughness and the frequent need for intrinsically hydrophobic materials.

[0054] Additive manufacturing techniques have successfully printed micro and nanoscale patterns in three-dimensions (3D) with high controllability and programmability to create hydrophobic surfaces. However, these processes can be time-consuming due to the trade-off between printing speed and structural complexity, and are typically used to create only two-dimensional (2D) structures. The present inventors determined inducing phase separation within materials post-printing has reduced printing time and increased damage tolerance of superhydrophobic surfaces, but the need for post-printing processing and sacrifices in programmability have hindered the broad adoption of this technique.

[0055] The present disclosure provides a method for forming a superhydrophobic coating. The method comprises aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas. The method comprises directing the mist to a substrate. The mist traverses to the substrate over a flight time. The method comprises decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles. The method comprises contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate. The superhydrophobic coating comprises the gel particles. The method according to the present disclosure can be straightforward to fabricate superhydrophobic surfaces using a marginally hydrophobic polymer and can enhance efficiency of the technique, printability, and / or control of the structure of the superhydrophobic surface. The method according to the present disclosure can enhance spatial control of the superhydrophobic coating.

[0056] Referring to FIG. 8, a method for forming a superhydrophobic coating is provided. The method comprises aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas at step 802. The solution can be liquid.

[0057] The polymer can comprise various polymers and / or monomers that can form gel particles. In various examples, the polymer can comprise a siloxane polymer, thermoplasticpolyurethane, polyvinyl alcohol, nylon, sucrose, cellulose, a protein, polyethyleneimine, polypropylene, and / or polyethylene. In certain examples, the polymer can comprise an ultraviolet (UV) polymerizable and / or crosslinkable polymer, such as, for example, an acrylate, a methacrylate, a polyester, a polycarbonate, a polydimethylsiloxane (PDMS) polymer.

[0058] The siloxane polymer can comprise a PDMS polymer. In certain examples, the polymer comprises disulfide-polydimethylsiloxane (DS-PDMS).

[0059] The solvent can comprise various solvents that are miscible with the polymer. The solvent can comprise an organic solvent, such as, for example, a non-polar solvent and / or a polar solvent. In various examples, the solvent can comprise a polar aprotic solvent. In certain examples, the solvent comprises at least one solvent selected from the group consisting of tetrahydrofuran (THF), dimethylformamide (DMF), N-Methyl-2-pyrrolidone (NMP), chloroform, methanol, ethanol, acetone, dimethyl sulfoxide (DMSO), acetonitrile, and ethyl acetate.

[0060] The solvent can comprises a vapor pressure of 0.1 mmHg or more, such as, for example, 1 mmHg or more, 10 mmHg or more, 100 mmHg or more, or 120 mmHg or more. The solvent can comprise a vapor pressure of 300 mmHg or less, such as, for example, 250 mmHg or less. The solvent can comprise a vapor pressure in a range of 0.1 mmHg to 300 mmHg, such as, for example, 1 mmHg to 300 mmHg or 100 mmHg to 300 mmHg.

[0061] In certain examples, the vapor pressure of the solvent can be balanced with the flight time, temperature, size of the droplets, and carrier gas used, with respect to the formation of gel particles. For example, a high vapor pressure solvent can lead to a reduction in flight time, reduction in temperature, and / or an increase in a size of the droplet. A low vapor pressure solvent can lead to an increase in flight time, an increase in temperature, and / or a decrease in a size of the droplets. Flight time may be balanced with desired patterning resolution. For example, increased flight time can lead to decreased patterning resolution.

[0062] The solution can comprise a first concentration of the polymer. In certain examples, the first concentration be less than the gelation concentration of the polymer. For example, the first concentration can be 0.62 volume fraction or less, such as, for example, 0.5 volume fraction or less, 0.45 volume fraction or less, 0.42 volume fraction or less, or 0.4 volume fraction or less. The first concentration can be 0.01 volume fraction or greater, such as, for example, 0.1 volume fraction or greater, 0.15 volume fraction or greater, or 0.2 volume fraction or greater. In various examples, the first concentration can be in a range of 0.01volume fraction to 0.62 volume fraction, such as, for example, 0.1 volume fraction to 0.5 volume fraction, all based on the total volume of the solution.

[0063] As used herein, “gelation” refers to refers to the process by which a solution comprising a polymer transitions from a liquid state to a solid-like, gelled state, where the solution does not flow freely under standard operating temperature and pressure. For example, “gelation” refers to the physical entanglement and / or chemical crosslinking of components in the solution. In this regard, the term “gelation,” as used in this specification, refers to physical entanglement of the polymer chains and / or the condition of the solution in which a component of the solution has chemically reacted to form new covalent bonds (e.g., new covalent bonds formed to create a polymer chain), new ionic bonds, new hydrogen bonds, new van der walls bonds, or combinations thereof. The polymer can form a three-dimensional network trapping the solvent or remaining liquid within the structure. The result is a material with properties intermediate between a liquid and a solid, such as elasticity (storage modulus) and the ability to retain shape.

[0064] The solution can comprise various other components depending on the application. For example, the solution can comprise a crosslinker, photo initiator, rheological agent, plasticizer, pigment, additional solvent, and / or other component.

[0065] The solution may be slightly hydrophilic or hydrophobic. For example, a drop-cast film prepared from the solution can exhibit a contact angle, with respect to a water drop placed on the film, of at least 70 degrees, such as, for example, at least 80 degrees, at least 90 degrees, at least 100 degrees, or at least 110 degrees. The drop-cast film prepared from the solution can exhibit a contact angle, with respect to a water drop placed on the film, of 150 degrees or less, such as, for example, 145 degrees or less, 140 degrees or less, 130 degrees or less, 120 degrees or less, or 110 degrees or less. The drop-cast film prepared from the solution can exhibit a contact angle, with respect to a water drop placed on the film, in a range of 70 degrees to 150 degrees, such as, for example, 80 degrees to 145 degrees, 90 degrees to 130 degrees, or 90 degrees to 120 degrees. The drop-cast film can be prepared by placing 5 pL of the solution on a polytetrafluoroethylene substrate and drying the solution to form a solid drop-cast film. Then, a water drop can be placed on the film and the contact angle of the drop-cast film can be measured by a contact angle goniometer.

[0066] The droplets can comprise a diameter of 100 nm or greater, such as, for example, at 150 nm or greater or 200 nm or greater. The droplets can comprise a diameter of 50 pm or less, such as, for example, 40 pm or less, 30 pm or less, 20 pm or less, 10 pm or less, 5 pm or less, or 1 pm or less. In various examples, the droplets can comprise a diameter in a range of100 nm to 50 m, such as, for example, 100 nm to 10 pm, and 100 nm to 1 pm. The diameter of the droplets can be an average diameter measured by optical microscopy.

[0067] In certain examples, the size of the droplet can be balanced with the flight time, temperature, vapor pressure of the solvent, and carrier gas used. For example, a large droplet diameter can lead to an increase in flight time, increase in temperature, and / or an increase in a vapor pressure of the solvent. A small droplet diameter can lead to a decrease in flight time, a decrease in temperature, and / or a decrease in a vapor pressure of the solvent.

[0068] The gas can comprise various gases suitable to form droplets of the solution. For example, the gas can comprise nitrogen, air, or a combination thereof. The gas can optionally comprise solvent vapor.

[0069] As used herein, a “mist” is meant to mean a substance comprising droplets of liquid that are suspended in a gas. Mist can vaporize or evaporate into vapor. Mist may not condense, as mist is already in the liquid phase. Mist can be generated with a suitable liquid droplet generating device such as, for example, an ultrasonic aerosolizer. Depending on the size and density of the droplets of liquid, mist can be visible to the naked eye. In various examples, the liquid comprises the solvent.

[0070] Referring again to FIG. 8, the method can comprise directing the mist to a substrate at step 804. The mist traverses to the substrate over a flight time. The flight time can be 1 second or less, such as, for example, 0.5 seconds or less, 0.1 seconds or less, 0.10 seconds or less, 0.009 seconds or less, 0.008 seconds or less, 0.007 seconds or less, 0.006 seconds or less, or 0.005 seconds or less. The flight time can be controlled by selecting a velocity of the droplets and / or distance to the substrate.

[0071] The method can comprise decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles at step 806. For example, the droplets can transition from a liquid state to solid-like gel state to form the gel particles. The damping factor (tan 5) is a ratio of a loss modulus (G”) to the storage modulus (G’) over relevant frequencies (e.g., 0.6 to 600 rad / s). The loss modulus (G”) and the storage modulus (G’) can be measured according to ASTM D4065. In various examples, the loss modulus (G”) and the storage modulus (G’) can be measured on a Bohlin Gemini Stress controlled rheometer at a temperature of 25 degrees Celsius and a frequency in a range of 0.6 to 600 rad / s.

[0072] The damping factor can decrease from greater than 1 to 1 or less, such as, for example, from greater than 1 to 0.9 or less, from greater than 1 to 0.8 or less, from greater than 1 to 0.5 or less, or from greater than 1 to 0.1 or less. The decrease in the damping factor can be due to the chemical bonds and / or physical-chemical interactions within the droplets.

[0073] In various examples, as the droplets transition to the gel particles, the loss modulus (G”) can decrease and approach zero. In certain examples, as the droplets transition to the gel particles, the storage modulus (G’) can substantially increase. In various examples, the gel particles can comprise a loss modulus (G”) that is less than a storage modulus (G’) of the gel particles.

[0074] In certain examples, decreasing the damping factor can comprise removing at least a portion of the solvent from the droplets by evaporation during the flight time to increase a concentration of the polymer within the droplets, thereby forming gel particles. For example, removing the solvent from the droplets by evaporation can increase the concentration of the polymer by 0.1 volume fraction or greater, such as, for example, 0.15 volume fraction or greater, 0.2 volume fraction or greater, or 0.3 volume fraction or greater, all based on the total volume of the droplets.

[0075] The increase in the volume fraction can cause the droplets to comprise a second concentration of the polymer after solvent evaporation. The second concentration of the polymer can be at least the gelation concentration of the polymer. For example, the second concentration of the polymer can be 0.62 volume fraction or greater, such as, for example, 0.65 volume fraction or greater, or 0.7 volume fraction or greater, all based on the total volume of the droplets. After the polymer meets or exceeds the gelation concentration of the polymer in droplets, the droplets can transition from a liquid state to solid-like gel state to form the gel particles.

[0076] The temperature of the mist can be controlled to facilitate the evaporation of the solvent. For example, a higher temperature can facilitate evaporation with high vapor pressure solvents, fast flight time, and / or large droplet sizes. The temperature of the mist can be in a range of -10 degrees Celsius to 200 degrees Celsius, such as, for example, 20 degrees Celsius to 170 degrees Celsius, 110 degrees Celsius to 170 degrees Celsius, 0 degrees Celsius to 100 degrees Celsius or 70 degrees Celsius to 90 degrees Celsius.

[0077] In certain examples, decreasing the damping factor of the droplets within the mist during the flight time comprises polymerizing the polymer.

[0078] Polymerizing the polymer can comprise exposing the droplets to electromagnetic radiation, such as, for example, UV electromagnetic radiation (e.g., 100 nm to 400 nm, such as, for example, 315 nm to 400 nm, 280 nm to 315 nm, or 100 nm to 280 nm).

[0079] In certain examples, the polymer can comprise a UV polymerizable polymer. As the droplets are exposed to the UV electromagnetic radiation, the polymer can polymerize andincrease in molecular weight. The droplets can increase in physical entanglements and the droplets can gel.

[0080] In various examples, the polymer can comprise a UV crosslinkable polymers (e.g., the solution would also contain a crosslinker). As the droplets are exposed to UV electromagnetic radiation, chemical (e.g.„ covalent) crosslinking of the polymers can initiate. Once substantially crosslinked, the droplets would form a gel.

[0081] In certain examples, the polymer can comprise UV polymerizable and crosslinkable polymers. As the droplets are exposed to UV electromagnetic radiation, simultaneous polymerization of the polymer and chemical crosslinking, can create a gel.

[0082] Referring again to FIG. 8, the method can comprise contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate at step 808. The superhydrophobic coating comprises the gel particles.

[0083] The gel particles can substantially retain their shape and / or may not coalesce or otherwise deform after deposition and contract with the substrate. For example, the gel particles can generally maintain a spherical shape due to surface tension effects. In various examples, the gel particles, on average, can comprise a sphericity of 0.8 or greater, such as, for example, at least 0.82, at least 0.84, at least 0.86, at least 0.88, at least 0.90, at least 0.92, at least 0.94, at least 0.95, at least 0.96, at least 0.97, at least 0.98, or at least 0.99.

[0084] The superhydrophobic coating can comprise a network of interconnected gel particles. Balancing the droplet size of the solvent, the flight time, temperature, vapor pressure of the solvent, and carrier gas used can lead to a desirable superhydrophobicity of the superhydrophobic coating.

[0085] Optionally, the mist and / or gel particles can be directed towards the substrate utilizing a nozzle. A sheath gas can be introduced into the nozzle. The mist and / or gel particles can be focused within the sheath gas within the nozzle to form a collimated stream of mist. The collimated stream of mist can be directed towards the substrate, which can provide enhanced control over the to-be-formed superhydrophobic coating.

[0086] Referring to FIG. 9, an article 900 is provided. The article comprises a superhydrophobic coating 902 and a substrate 904, which can be in contact with the superhydrophobic coating 902. The superhydrophobic coating 902 can cover an entire surface 904a of the substrate 904 or less than all of the surface 904a of the substrate 904. The superhydrophobic coating 902 can be produced by the method according to the present disclosure.

[0087] The superhydrophobic coating 902 can comprise gel particles that form a three dimensional network. The gel particles can form a micro- and / or nano-structure that can lead to an enhance hydrophobicity of the superhydrophobic coating 902 that is not achievable with the polymer used in the gel particles in a drop-cast film. For example, the superhydrophobic coating 902 can exhibit a contact angle of 150 degrees or greater, such as, for example, 160 degrees or greater. The contact angle can be measured with a contact angle goniometer.

[0088] The superhydrophobic coating 902 can exhibit a sliding angle of 10 degrees or less, such as, for example, 5 degrees or less, 4 degrees or less, 3 degrees or less, or 2 degrees or less.

[0089] The superhydrophobic coating can exhibit a surface roughness of 0.5 pm or greater, such as, for example, 1 pm or greater. The surface roughness can be influenced by the size of the gel particles and / or amount, if any, of deformation of the gel particles after contacting each other and / or the substrate 904. The surface roughness can be measured by an area arithmetical mean height using an optical profilometer.

[0090] The superhydrophobic coating can be patternable with dimensions of 25 microns or greater. For example, the line width and line spacing during additive manufacturing can be 25 microns or greater.

[0091] The article 900 can be a device with a self-cleaning surface, a device with a water-repellent, a device for droplet manipulation, a microreactor, a mixer, an water-oil separator, a device for retardation of droplet evaporation, a device for protein stabilization, a device for protein storage without refrigeration, a non-wetting display, or other device.

[0092] The method can be an additive manufacturing method. As used herein, “additive manufacturing” means a process of joining materials to make objects from 3D model data as opposed to subtractive manufacturing methodologies. For example, additive manufacturing can comprise aerosol jetting.

[0093] Aerosol jetting utilizes a focused stream of aerosolized material to deposit precise patterns onto a substrate. In contrast to traditional inkjet printing, which relies on liquid droplets, aerosol jetting atomizes a material into a fine mist of droplets. This mist can then be carried by a gas stream and focused through a nozzle, allowing for high-resolution, noncontact deposition. Aerosol jetting can be used on flat and / or textured surfaces.

[0094] Referring to FIG. 10, an additive manufacturing system 1000 is provided. The system 1000 can be configured to perform the method for forming a superhydrophobic coating according to the present disclosure.

[0095] The system 1000 can comprise a computer system 1006, a platen-based platform 1008, a nozzle 1010, a reservoir 1012, an ultrasonic aerosolizer 1014, a gas source 1016 for the aerosolizer, and a sheath gas source 1018 for the nozzle 1010. In various examples, an analyzer, additional gas sources, reservoirs, aerosolizers, lights (e.g., UV lights), and / or nozzles may be added to the system 1000 to increase the printing capabilities of the system 1000. For simplicity, only one aerosolizer and nozzle is shown in FIG. 10.

[0096] The system 1000 can be capable to print material onto a substrate 1004 on the platform 1008 using the reservoir 1012, ultrasonic aerosolizer 1014, and nozzle 1010 to form an article 1050.

[0097] In various examples, the nozzle 1010 can be coupled to a gantry 1020 or other robotic device to support and / or move the nozzle 1010 relative to the platform 1008. Optionally, the nozzle 1010 can be coupled to a motor assembly or other movement assembly configured to translate and / or rotate the gantry and / or robotic device. The nozzle 1010 can comprise an orifice diameter in a range of 500 microns to 300 microns, such as, for example, 100 microns to 250 microns or 100 microns to 150 microns.

[0098] In certain examples, the platform 1008 can be moved with a motorized stage or with a robot to move the platform 1008 relative to the nozzle 1010. The platform 1008 can be heated to elevated temperatures above room temperature (e.g., 20 degrees Celsius), such as, for example, to a temperature of 20 degrees Celsius or greater, 60 degrees Celsius or greater, 90 degrees Celsius or greater, or in a range of 60 degrees Celsius to 90 degrees Celsius.

[0099] The computer system 1006 can be in signal / data communication with the gas source 1016, reservoir 1012, aerosolizer 1014, nozzle 1010, platform 1008, sheath gas source 1018, and / or the gantry 1020 (such as via a wired and / or wireless data bus or link). The computer system 1006 can be configured through programming to control the operation of the gas source 1016, reservoir 1012, aerosolizer 1014, nozzle 1010, platform 1008, sheath gas source 1018, and / or the gantry 1020. The computer system 1006 can also receive data from and send data (e.g. control data) to the gas source 1016, reservoir 1012, aerosolizer 1014, nozzle 1010, platform 1008, sheath gas source 1018, and / or the gantry 1020. The components in the system 1000 may be in communication with the computer system 1006 via any suitable type of data bus (e.g., parallel or bit serial connections).

[0100] The computer system 1006 can comprise one or more processors operatively coupled to one or more non-transitory memories. The processor may comprise one or multiple processing cores. The memory can comprise primary storage (e.g., main memory that isdirectly accessible by the processor, such as RAM, ROM processor registers or processor cache); secondary storage (e.g., SSDs or HDDs that are not directly accessible by the processor); and / or off-line storage. The memory stores computer instructions (e.g., software) that are executed by the processor. The processor can be configured (through execution of the software stored in the memory) to control operation of the gas source 1016, reservoir 1012, aerosolizer 1014, nozzle 1010, platform 1008, sheath gas source 1018, and / or the gantry 1020 to thereby control the deposition of the droplets and / or gel particles through the nozzle 1010. For example, the processor can control the flow rate of gas into the reservoir 1016, amount of aerosolization, flow rate of sheath gas, and / or the pose of the nozzle 1010 relative to the platform 1008.

[0101] The memory can store a digital or electronic computer model of the superhydrophobic coating 1002 to be manufactured by the additive manufacturing process. The computer model can be loaded locally into the memory or can be downloaded from another device (e.g., another computer device, cloud) that is in data communication with the computer system 1006. To that end, the computer system 1006 may comprise a network interface controller (NIC) that connects the computer system 1006 to a computer network. The computer model can be in a variety of different digital or electronic formats, such as an STL file, a OBJ file, a FBS file, a COLLADA file, a 3DS file, an IGES file, a STEP file, a VRML / X3D file, a point cloud, or another 3D model file format type.

[0102] The processor can be configured to create machine path instructions (e.g., G-code instructions) for the computer model. The machine path instructions can be stored in the memory. The machine path instructions can comprise print parameters and can be executed by the processor to cause the processor to control the operation (e.g., pose, flow rate, aerosolization) of system 1000 or other device.

[0103] The depositing of the gel particles using the nozzle 1010 can be repeated as necessary to additively form a superhydrophobic coating 1002. For example, the processor can control the nozzle 1010 to deposit the gel particles in order to additively form a super hydrophobic coating 1002 based on the computer model.

[0104] The platform 1008 can be configured for mechanically supporting and / or holding the substrate 1004 during additive manufacturing. The platform 1008 can comprise a motor and / or actuator that can move the platform in 3D space as needed. The platform 1008 can be in signal and / or data communication with the computer system 1006.EXAMPLES

[0105] Various aspects, benefits and features that are potentially realizable through implementation of the present invention will be more fully understood by reference to the following examples, which provide illustrative non-limiting aspects of the invention. It is understood that the invention described in this specification is not necessarily limited to the examples described in this section.

[0106] The Examples below illustrate methods for creating superhydrophobic surfaces by aerosolizing polymer solutions into micrometer-sized droplets and converting them into microgel particles during spatially controlled deposition using an aerosol jet printer. The polymer solutions composed of marginally hydrophobic disulfide-polydimethylsiloxane (DS-PDMS) in three solvents with varying vapor pressures. The experiments, combined with an analytical model, demonstrate that solvents with high vapor pressures evaporate from the droplets during flight from the printer nozzle to the substrate. This evaporation can increase the DS-PDMS volume fraction in the droplets above the polymer gelation threshold. As a result, the droplets transform into microgel particles. This transformation can lead to the formation of rough, superhydrophobic surfaces.

[0107] Solvents with lower vapor pressures may not evaporate sufficiently and the DS-PDMS volume fraction may not reach the gelation threshold in the flight time used. These droplets may coalesce upon deposition, producing smooth surfaces with hydrophobicity similar to intrinsic DS-PDMS. Heating the surfaces to 90 °C or above eliminates superhydrophobicity by de-gelling the DS-PDMS, allowing droplet coalescence. Potential applications of this method include droplet manipulation, microreactors for reactant mixing, water-oil separation, and retardation of droplet evaporation. It is believed that increasing the temperature of the gas, sheath gas, platform, and / or nozzle temperature, and / or flight time can lead to the solvents with lower vapor pressure sufficiently evaporating to form gel particles.

[0108] The Examples herein present straightforward methods to fabricate superhydrophobic surfaces using a marginally hydrophobic polymer. This can be achieved by depositing polymer microgel particles onto a substrate with high spatial control and programmability. The fabrication process described in the Examples and illustrated in FIG. 1, involves aerosolizing polymer solutions into micrometer-sized droplets and depositing them onto substrates in specific patterns using aerosol jet (AJ) printing, a microfabrication technology. This technique can produce superhydrophobic surfaces through a simple method that requires no post processing. The AJ printing process offers precise control over the shape and location of superhydrophobic structures, with feature sizes as small as 10 pm. This precisioncan enable a wide array of applications. Additionally, the Examples demonstrate significant control over the level of hydrophobicity, which is uncommon in other scalable techniques.

[0109] The polymer solutions used for the AJ printing process consist of disulfidepoly dimethylsiloxane (DS-PDMS) (CA = 99° ± 1°) dissolved in solvents. The inventors selected solvents with different vapor pressures (Pv) to produce various effects in the resulting printed structure. The solvents used were tetrahydrofuran (THF) with=127.5 mmHg, dimethylformamide (DMF) with Pv DMF= 2.8 mmHg, and N-Methyl-2-pyrrolidone (NMP) withNMP= 0.24 mmHg. At low volume fractions ((|>) of polymerP°lymersolutions are liquid-like but gel at higher <bDS. PDMS, with the gelation threshold defined as 4*f^s_PDMS- During printing, if <bDS. PDMSin the droplets rises abovegels in the droplets. This can prevent the droplets from coalescing upon deposition, resulting in a rough and superhydrophobic surface (left side in FIG. 1). Potential applications of this method can be droplet manipulation, microreactor technology, water-oil separation, and retardation of droplet evaporation. Conversely, if <bDS. PDMSin the droplets remains belowthe droplets coalesce post-deposition, creating a smooth surface without superhydrophobicity (right side in FIG. 1). DS-PDMS de-gels at temperatures 90 °C and re-gels upon cooling, allowing for selective removal of superhydrophobicity after fabrication.

[0110] FIG. 1 illustrates a method and mechanism for creating superhydrophobic surfaces through spatially controlled deposition of polymer solution droplets. When using a solvent with high vapor pressure (e.g., ~102mm Hg), rapid evaporation causes polymer to gel within the droplets during their flight from the nozzle to the substrate, resulting in polymer microgel particles that create a rough, superhydrophobic surface. Conversely, with a low vapor pressure solvent (e.g., -10'1mm Hg), the polymer solution remains liquid during flight, and the droplets coalesce on the substrate, forming a smoother, non-superhydrophobic surface.[OHl] Determination of Polymer Gelation Volume Fraction

[0112] To determine 4*|^S_PDMS, the inventors first dissolved DS-PDMS in the solvents at an initial volume fractionglass vials. The polymer solutions behaved as liquids and flowed freely under gravity when the vials were flipped as illustrated in FIG.2 A. Next, the inventors evaporated the solvents at 21 °C, 60 °C and 60 °C for THF, DMF and NMP, respectively, until the polymer solutions no longer flowed under gravity when the vials were inverted as illustrated in FIG. 2B. The inventors assumed that the bulk polymersolutions were in a gel state when they did not flow. The inventors also assumed that if the bulk polymer solutions with <bDS. PDMSresisted flow upon inversion, then a droplet with the same (|)DS_pDMSwould also resist flow. The threshold volume fraction in these gelled polymer solutions was ^(QS-PDMS, THF) ~ 0- 2 ± 0.02, ^(QS-PDMS, DMF) ~ 0- 5 ± 0.04, and±003. Higher solvent evaporation temperatures were chosen for DMF and NMP because Pv DMFand Pv NMPare very low, and the inventors wanted to speed up the evaporation process.

[0113] Estimation of the Probability of Droplet Coalescence After Generation and Deposition on the Substrate

[0114] AJ 3D printing was used to aerosolize the polymer solutions with low volume fractions into droplets using ultrasonication. These droplets were deposited on a substrate with high spatial precision, as shown in FIG. 3 A. Nitrogen was used as a carrier gas and transported these droplets through a tube to the deposition head. Nitrogen was also used as the sheath gas and focused the incoming stream of droplets. These droplets exited the print nozzle as a tightly focused, collimated beam and impacted the substrate. During AJ printing, if the solvents evaporated quickly, the <bDS. PDMSwithin each droplet increased rapidly, leading to polymer gelation when <bDS. PDMS> ^DS-PDMS- polymer solutions gelled before reaching the substrate, the gelled droplets resisted flow and coalescence during flight and deposition. As a result, the droplets retained their spherical shapes and created a rough, superhydrophobic surface as illustrated in the left side of FIG. 1. Conversely, if the solvents evaporated slowly, the polymer solutions in the droplets remained liquid during flight and deposition, leading to droplet coalescence and a smooth printed surface as illustrated on the right side of FIG. 1. In this scenario, the solvents continued to evaporate from the printed surface, causing the polymer to eventually gel and lock in the smooth surface, which did not display superhydrophobicity. Therefore, the resulting microstructure of the AJ-printed surface using concentration-dependent gelling polymers depended on the timescales of solvent evaporation relative to the droplet flight time ( / night) from formation at the nozzle to deposition on the substrate.

[0115] To determine the initial radii range of droplets within which DS-PDMS solutions could transition from liquid to gel during tflight, the <bDS. PDMSwas estimated during the printing process using a droplet evaporation model. Before the introduction of sheath gas, the carrier gas environment surrounding the droplets is expected to be saturated with solventvapors, which hinder solvent evaporation, keeping the droplet radii constant over time. Once the droplets enter the AJ printer head and nozzle, solvent evaporation begins as illustrated in FIG. 3 A. Assuming the droplets are spherical and that DS-PDMS does not affect solvent evaporation, the Stefan-Fuchs model was used to estimate the solvent evaporation rate (ie., solvent mass loss per unit time) starting from the nozzle entry (Region I in FIG. 3 A). The Stefan-Fuchs model is shown in Equation 1 below:

[0116] Equation 1ma= -4TtRaDvptotailn(l + BM~),where Rais the radius of droplet, Dv, is the diffusion coefficient of the vapor phase, and BMis the Spalding mass transfer number. The total mass density of the gas-vapor mixture was determined according to Equation 2 below:

[0117] Equation 2:where Mvand Pv(Mgand Pg) are the molecular weight and the partial pressure of the vapor phase, which is the solvent (the gas phase, which is nitrogen, for Regions I & II as illustrated in FIG. 3 A), respectively. Note, the droplets leave the nozzle in Region III of FIG. 3 A, where the gas phase is air instead of nitrogen.

[0118] The Spalding mass transfer number is calculated according to Equation 3 below:

[0119] Equation 3where pvand pv mare densities of the vapor phase in the vicinity of the droplets and in free space, respectively, and pg gis the density of the ambient gas, which is nitrogen in Region I & II illustrated in FIG. 3 A.

[0120] Furthermore, the droplet stream is assumed to be collimated starting from the nozzle region where sheath gas is introduced. The vapor density away from the droplets is expected to bepv / = -]pv sbecause the gas flow rate ratio between the carrier gas and the sheath gas is set to 1:2, and the carrier gas is presumed to be saturated with solvent vapors. When the droplet flight and the solvent diffusion timescales are comparable, the gas-vapor mixture would diffuse into the sheath gas during tflight. If solvents do not have sufficient time to diffuse, then the solvent vapor densities away from the droplets (at the edges of sheath gas) could be pv r~ 0, which would not change the relative magnitude of the estimation fordifferent solvents. Region I in FIG. 3 A, which is the wider part of the nozzle, has an average diameter ~ 650 pm and a length ~ 20.5 mm (inclusive of the connector and the thicker part of the nozzle). Region II in FIG. 3 A, which is the narrower part of the nozzle, has a diameter « 150 pm and a length « 4.5 mm. Region III in FIG. 3 A is the distance between the nozzle and the substrate, which is ~ 2 mm. Given the constant gas flow, the different diameters of Regions I and II result in varying flight speeds of the droplets in those regions, providing the total flight time for the droplets to reach the substrate, Zflight= 5.5* 10'6s. A small timescale was selected as dt = 1 x 10' s to calculate the volume fraction change. The relationship between <bDS. PDMSand dt can be expressed as Equation 4 below:

[0121] Equation 4where an initial volume fraction U -r UlVI of 0.041 ± 0.002 or 0.005 ± 0.001 has been used for different solvents specified later.

[0122] The curves in FIGs. 3B-3D show <bDS. PDMSin the droplets as a function of time for various initial droplet radii and solvents. The <bDS. PDMSwas plotted until the droplets reach ^DS-PDMS’ indicated by the horizontal dashed line in the plots, and it was assumed that once DS-PDMS solutions gel within the droplets, the droplet radii stop changing over time. The vertical dashed line in each plot represents Zflightand establishes the upper limit for the initial droplet radius for each solvent within which DS-PDMS solutions could gel during the flight. The calculations show that (DS-PDMS, THF) solutions in droplets are expected to gel before the droplets arrive at the substrate, with a relatively large upper limit in radius (« 8 pm) due to the fast evaporation of THF. The slower evaporation of (DS-PDMS, DMF) and (DS-PDMS, NMP) solutions lead to gel droplets having a smaller upper limit in radius (« 1 pm and ~ 0.3 pm, respectively), with any larger droplets still containing liquid solutions. Since the droplet radii generated with the ultrasonic aerosolization range from 0.5 to 2.5 pm, it is believed that (DS-PDMS, THF) solution will gel in all droplets by the time the droplets reach the substrate and retain their spherical shapes without coalescing. It is believed that the printed surfaces will comprise these spherical gel droplets and display a large enhancement in hydrophobicity compared to a smooth surface of the polymer. It is believed that (DS-PDMS, DMF) solution will gel within a fraction of the droplets with ’"lltial« 0.5 — 1 pm but to stayas liquid in droplets with larger radii that would coalesce upon arriving at the substrate. It is believed that the morphology of the printed surfaces will consist of mostly contiguous polymer film interspersed with a limited number of spherical droplets, exhibiting a limited enhancement over the intrinsic hydrophobicity of the polymer. It is believed that (DS- PDMS, NMP) solution in all droplets will remain as liquid, and the droplets to coalesce upon deposition on the substrate. Thus, it is believed that the printed surfaces will be smooth polymer surfaces and show negligible enhancement in hydrophobicity compared to DS- PDMS. Although aerosol evaporation was not directly measured, the predictions are based on the analytical model. These predictions are validated experimentally herein.

[0123] Characterization of Surface Morphology and Hydrophobicity

[0124] The intrinsic hydrophobic characteristics of DS-PDMS were characterized by preparing a drop-cast film using (DS-PDMS, THF) solution. After solvent evaporation, the drop-cast film was smooth and free of microscale features as illustrated in FIG. 11 with a measured CA = 99° ± 1°. DS-PDMS surfaces were fabricated with three different solvents (THF, DMF, and NMP) by AJ printing with an initial volume fraction=0.041 ± 0.02. To investigate the effect of this initial volume fraction on the printed surface morphology, another group of surfaces with a lower ^(DS-PDMS THF)=^ 005 ± 0.001 was fabricated. The printed surface morphology and hydrophobic characteristics were characterized using scanning electron microscopy (SEM) imaging and CA measurement, respectively as illustrated in FIGs. 4A-D.

[0125] The SEM images of a printed surface utilizing (DS-PDMS, THF) solutions show the surface comprises of micrometer-sized spherical particles as illustrated in FIG. 4A. There was minimal congealing between adjacent polymer spheres, indicating that DS-PDMS solutions in all droplets gelled prior to reaching the substrate. These surfaces exhibited superhydrophobicity with a high CA = 169° ± 1° and a low SA = 1.7° ± 0.1°. The advancing contact angle (ACA) is 176° ± 1° and the receding contact angle (RCA) is 163.9° ± 0.4°. Both ACA and RCA were measured just before the droplet slid as illustrated in Table 1 below:

[0126] Table 1: The static and dynamic contact angles from surfaces created using DS- PDMS solutions with THF, DMF and NMP as solvents

[0127] The printed surfaces utilizing (DS-PDMS, THF) solutions had a surface roughness of 1.35 pm ± 0.07 pm (area arithmetical mean height).

[0128] Surfaces fabricated with (DS-PDMS, DMF) solutions were relatively smooth and homogeneous with scattered, embedded microspheres as illustrated in FIG. 4B. These samples exhibited significantly weaker hydrophobicity with CA = 110° ± 3° (still larger than the CA of intrinsic DS-PDMS), SA = 56° ± 5°, ACA = 118.9° ± 0.5°, and the RCA = 98° ± 8° as shown in Table 1. The surface roughness was small 0.12 pm ± 0.02, confirming the smoothness of the surfaces. It is believed that (DS-PDMS, DMF) solution was in a liquid phase in the majority of the droplets when they arrived at the substrate as suggested by the solvent evaporation from droplet model. When these droplets impacted the substrate, they spread and coalesced with other droplets.

[0129] The scattered droplets on the surface in FIG. 4B originated from a technical artifact associated with AJ printing known as overspray. When droplets approached the substrate, the flow lines began to diverge, and the droplets were propelled forward by momentum rather than carrier flow. If the droplets were too small, they did not have enough momentum to impact the surface directly beneath the nozzle and were carried by the diverging flow lines for a time until they reached the substrate. These scattered droplets on the substrate are called overspray. These overspray droplets landed on the substrate adjacent to the main printed path and had much sparser spatial density. Because of their small size, it is likely that these droplets gelled before colliding with the substrate. This impeded their ability to recombine with an adjacent surface of gelled or partially gelled DS-PDMS solutions, leading to the partly embedded spherical droplets in an otherwise homogeneous surface seen in FIG. 4B. It is believed that due to this sparsely populated collection of gelled droplets that the hydrophobicity of these samples is greater than that of intrinsic DS-PDMS.

[0130] To substantiate this hypothesis, surfaces were printed using the same (DS-PDMS, DMF) solution with ^(DS-PDMS DMF)=^ 041 ± 0.002 but with a larger nozzle diameter of 300pm, in contrast to the previous surfaces printed with a 150 pm nozzle as illustrated in FIG.12A-F. It was observed these printed surfaces possessed a lower number density of overspray droplets owing to the wider printed line width as illustrated in FIGs. 12A, 12B, 12D and 12E, decreasing the CA to 98° ± 2° compared to surfaces printed with an identical polymer solution but a smaller diameter nozzle as illustrated in FIG. 12F. This observation highlights that besides the solvent, printing parameters including nozzle size and platen temperature can also be leveraged to tune the morphology and wetting properties of the printed surfaces.

[0131] The printed surfaces fabricated using (DS-PDMS, NMP) solutions with^(DS-PDMS NMP)=0041 ± 0.002 were very smooth with a surface roughness = 0.009 ± 0.006 pm with no observable spherical droplets as illustrated in FIG. 4C. The CA = 99° ± 3° is similar to that of intrinsic DS-PDMS. The observed non-uniform coloration (lighter vs. darker regions) within the SEM image could be due to differences in polymer thickness, stemming from the reflow of polymer solution after deposition on the substrate.

[0132] We note that the experimentally observed printed surface microstructure and hydrophobicity are well captured by the analytical model based on droplet evaporation and validate our hypothesized mechanism behind printed surface superhydrophobicity. For the samples printed with (DS-PDMS, THF) solution, the cross-sectional SEM images illustrated in FIGs. 15A-15C show that the printed structure is entirely composed of polymer spheres, not just at the surface. This suggests good wear resistance, although this was not explicitly tested in this work. The chemical stability of the superhydrophobic materials depends on the polymer. Therefore, the printed structures may not be resistant to solvents like alcohols, as DS-PDMS is not resistant to these solvents.

[0133] To further corroborate that the superhydrophobicity of printed surface is due to gelling of polymer solutions in the droplets from solvent evaporation, we evaluated the droplet radii distributions as illustrated in FIG. 4E. These distributions were measured from the SEM micrographs of the printed surfaces shown in FIG. 4 A and FIG. 4B. The surfaces were created using (DS-PDMS, THF) and (DS-PDMS, DMF) solutions, respectively. The average droplet radii for the surfaces printed using (DS-PDMS, THF) and (DS-PDMS, DMF) solutions are 0.4 ± 0.1 pm and 0.19 ± 0.05 pm, respectively. Because only the overspray droplets are small enough to reach gelation and retain their spherical form, the average droplet radius in surfaces printed with (DS-PDMS, DMF) solution is much smaller than that in surfaces printed with (DS-PDMS, THF) solution. For the droplets within which DS-PDMSsolutions gel, the final droplet radii are a function ofSince the polymer content in the droplet is constant before and after solvent evaporation according to the following Equation 5:

[0134] Equation 5:

[0135] To validated the findings, films were printed using solutions withT(JJo-r Ulvl. - 1m nri )f 0.041 ± 0.002 andT InttrrJ,=0.005 ± 0.001. The drop1let radii distribution obtained from SEM micrographs of the printed surfaces is shown in FIG. 4F. Assuming all other variables are held constant, the radii of the droplets was expected to shrink by a factor of 0.34 relative to their radii for solutions withTTin.(U -r Ulvl. 1 nr ) = 0.041 ± 0.002 when theyJreach the substrate. SimilarlyJ, ’ under identical conditions, the radii of the droplets generated using solution with= 0.005 ± 0.001 was expected to contract by a factor of 0.17. For example, the1 J 1 7droplets in the printed surface fabricated using solutions with ^"OS-'I-DMSTHF)= 0.005 ± 0.001 should be half the radii of the droplets in the printed surfaces created using solutions with (f i'mK nm.=0.041 ± 0.002. Based on the data from FIG. 4F, the mean droplet radius in the printed surfaces using solutions with ^(DS^DMS THF)=^ 005 ± 0.001 is 0.19 ± 0.05 pm, and that withT(U -r Ulvl. T 1 nUrI )=0.041 ± 0.002 is 0.4 ± 0.1 p ‘ m,7for a ratio of 0.51.

[0136] The disulfide (DS) bonds in DS-PDMS are dynamic, breaking when the polymer is heated to 90 °C and reforming when cooled well below that temperature. This dynamic bonding capability can be exploited to alter the microstructure and hydrophobic characteristics of AJ-printed surfaces. This behavior facilitates the flowability of previously gelled DS-PDMS droplets, leading to their coalescence. Consequently, an AJ-printed superhydrophobic surface can undergo post-printing modifications. A superhydrophobic surface fabricated using (DS-PDMS, THF) solutions was heated to90 °C for 30 min. This treatment smoothed the surface roughness and eliminated superhydrophobicity, reducing CA from 169° ± 1° to 99° ± 2°, similar to the intrinsic CA of DS-PDMS as illustrated in FIG. 5 A. In comparison, surfaces printed with (DS-PDMS, DMF) solutions showed that overspray droplets merged with the underlying smooth surface, lowering the CA from 110° ± 3° to 98° ± 2° after heating as illustrated in FIG. 5B. Surfaces printed with (DS-PDMS, NMP)solutions exhibited minimal changes in morphology and CA before and after heating as illustrated in FIG. 13, likely because the surface was already smooth and similar to intrinsic DS-PDMS. These observations underscore that superhydrophobicity primarily arises from the morphology and microstructure created by droplets. Furthermore, this approach introduces a method for locally programming superhydrophobicity through controlled heating, thereby expanding the capabilities of printed surfaces.

[0137] Applications

[0138] Various applications can be enabled by the highly programmable and versatile AJ-printed superhydrophobic surfaces. AJ can create channels ~ 25 pm in width for droplet manipulation, which can be promising in microfluidic manipulation, drug screening, and indroplet chemical synthesis. As an illustrative example, an ‘S’-shaped channel was printed for water droplets to travel, as shown in FIG. 6A. Two meandering lines, each ~ 1 mm wide, were printed next to each other on a bare silicon wafer. The ~ 1 mm space between the two printed lines provides a narrow silicon channel that can be wetted by a water droplet as illustrated in FIGs. 14A. The spacing is designed to accommodate the water droplets with radii arising from pipette deposition. When the wafer is tilted to 45°, the droplet is guided by the printed structure and follows the meander pattern. One potential use case for this technique is droplet mixing for microreactions. FIG. 6B shows an arc-shaped channel in which a droplet is dispensed at each end of the arc. When the wafer is tilted, the two droplets follow the channel until they meet at the reservoir and mix, facilitating controlled microscalevolume reactions. Moreover, a tapered channel was fabricated to direct droplet movement without any wafer tilting or applied agitation force as illustrated in FIG. 6C. A dispensed water droplet would spontaneously move toward the wider end of a tapered channel because the energy state at the wider end of the channel is lower than at the narrower end for a given droplet size.

[0139] The superhydrophobic DS-PDMS surface can also extract oil from a droplet as illustrated in FIG. 6D. The oil is attracted to the DS-PDMS while the water is repelled by it due to its hydrophobicity. When an oil-water mixture contacts the superhydrophobic surface, the water beads up due to the water contact angle, while the oil spreads out and can penetrate the surface. This oil-water separation effect could possibly help address environmental pollution caused by oil-water mixing and the issue of oil-contaminated water in industrial production.

[0140] A method for reducing the evaporation of microdroplets was demonstrated. As illustrated in FIG. 6E, a DS-PDMS patch printed with circles where the silicon is left exposed. These exposed circles act as wells for droplet placement. The size of the circles can determine the CA of the droplet. Due to the higher CA, a droplet dispensed in these reservoirs will have a much slower evaporation rate than droplets dispensed on the silicon. In this case, two 5 pL water droplets were placed on the reservoir and on the silicon wafer. The evaporation time was approximately 63% longer for the high contact angle droplet placed on the printed well. This technique can be applied in biomedical technologies, where precise control of the evaporation rate is crucial for maintaining the concentration of substances in a droplet.

[0141] Conclusions

[0142] A robust method to fabricate superhydrophobic surfaces was developed using AJ printing with DS-PDMS, a polymer that is marginally hydrophobic (CA ~ 99° ± 1°) and gels at higher concentrations. The printed surfaces exhibit superhydrophobicity (CA ~ 160° ± 2°) when they have sub-micron to micron-scale roughness due to non-coalescing droplets. This morphology can be influenced by the vapor pressure of the solvents used. High vapor pressure solvents, like THF, cause sufficient evaporation during printing, leading to gelation of polymer solutions in the droplets, suppressing droplet coalescence and forming a rough surface. Low vapor pressure solvents, like NMP, do not evaporate sufficiently, causing the polymer solutions within the droplets to remain liquid, resulting in smooth surfaces due to droplet coalescence. Heating the printed surfaces to90 °C can eliminate superhydrophobicity by causing DS-PDMS to de-gel and droplets to merge, smoothing the surface.

[0143] While we demonstrated the technique for producing superhydrophobic structures using DS-PDMS and certain solvents, this method can be applied to various other polymers and solvents according to the present disclosure. It can also be adapted with different print parameters, such as nozzle diameter and platen temperature. Additionally, the technique’s versatility allows for scaling to larger surfaces while maintaining consistent droplet sizing.

[0144] Experimental Methods

[0145] Referring to FIG. 7, the chemical structures of the three reactants used in the synthesis of disulfide-polydimethylsiloxane (DS-PDMS) are shown: aminopropyl terminated polydimethylsiloxane (PDMS-NH2), isophorone diisocyanate (IPDI), and bis(2-hydroxy ethyl) disulfide (HEDS) are provided.

[0146] DS-PDMS Synthesis'. The synthesis method is a modified version of the previously reported method. The three reactants used are: aminopropyl terminated polydimethylsiloxane (PDMS-NH2, 20-30 cSt, Gelest Inc.), isophorone diisocyanate (IPDI, Tokyo Chemical Industry Co., Ltd.), and bi s(2-hydroxy ethyl) disulfide (HEDS, Tokyo Chemical Industry Co., Ltd.) (Figure 7). First, 2 g of PDMS-NH2, 0.89 g of IPDI, and 0.31 g of HEDS were each dissolved in 4 mL, 10 mL, and 10 mL of acetone, respectively. All solutions were bubbled with nitrogen for 5 minutes to remove any dissolved oxygen. The IPDI solution was then added at a rate of 80 pL min'1to the PDMS-NH2 solution at 60 °C using a syringe pump (Harvard Apparatus, PHD 2000). After the complete addition of IPDI solution, the mixture was reacted for 3 hours. Subsequently, the HEDS solution was added at 80 pL min'1to the mixture and reacted for an additional 5 hours. Finally, the synthesized DS-PDMS was collected by slowly evaporating the acetone.

[0147] DS-PDMS solutions'. The DS-PDMS solutions were prepared by dissolving the synthesized DS-PDMS in a designated solvent at a specific concentration. For instance, to achieve an initial concentration of0.041 ± 0.002, 90 mg of DS-PDMS (density ~ 1.1 g mL'1) was dissolved in 2 mL of THF. The mixture was magnetically stirred for 30 min to ensure complete dissolution of the polymer. Given that DS-PDMS has better solubility in THF compared to DMF, the (DS-PDMS, DMF) solution was magnetically stirred for 1 h followed by an additional 30 min of bath sonication (40 kHz, Cole-Parmer 08895-01).

[0148] Aerosol Jet Printing'. The surfaces were 5 mm by 5 mm patches consisting of two printed layers. There layers were created by repeatedly printing parallel lines with a pitch small enough to ensure the lines overlapped, forming a continuous surface. The pitch between lines was 80 pm. The second layer was printed directly on top of the first, with its lines oriented perpendicular to those of the first layer, ensuring fully coverage of the underlying layer. The total thickness of the two-layer patch was ~35 pm. The surfaces were printed on a silicon wafer spun-coated with a water-soluble release layer of poly (acrylic acid) (PAA). The print was performed with a sheath flow of 50 seem N2 and a carrier flow of 18 seem N2. The print surfaces were heated to 40 °C using a heated platen.

[0149] Measurement Techniques'. CA was measured using a Contact Angle Goniometer (Rame-Hart, Model 100-00-115). AC A, RCA and SA were measured using the goniometer (Attension Theta, Biolin Scientific). Each measurement involved placing a 5 pL distilled water droplet on a 5 mm by 5 mm printed patch. The CA measurement was repeated threetimes for each surface, and the reported CA value is the average of these measurements. The morphology of the printed surfaces was imaged using a Scanning Electron Microscope (Phenom XL). Each surface was coated with a 2 nm thick gold layer using a sputter coater (Quorum Q300TD) before imaging. SEM imaging was conducted at 10 kV and a vacuum level of 10 Pa. Particle sizes were measured from a random selection of particles in the SEM images using ImageJ by determining the circular area of individual particles with the region of interest feature. Surface roughness was measured using Keyence VK-X3000. Surface variation of macrostructures is caused by the shapes of the printed lines. The effect of these variations on surface roughness was eliminated in analysis through surface fitting.

[0150] Demonstration: For droplet mixing demonstration as illustrated in FIG. 6B, one of the water droplets was colored with green food dye (Cherry sea). Water droplets of 10 pL, both with and without food dye, were placed at the beginning of the channel with the wafer tilted at ~ 45°. For the water-oil separation demonstration FIG. 6D, 5 mL of vegetable oil was mixed with 0.1 g oil dye (Oil Red O, Thermo Scientific Chemicals), and the dyed oil was then mixed with water at a ratio of 1:20 by volume. A 5 pL droplet of the water-oil mixture was then placed on a superhydrophobic surface fabricated using (DS-PDMS, THF) solutions with <(DS. PDMS THF)- 0.041 ± 0.002).

[0151] Diffusion Timescale of Solvent Vapor in Sheath Gas

[0152] To evaluate the evaporation environment of the droplets during AJ printing, the timescale for THF vapor to diffuse from the carrier gas to the sheath gas in the printer nozzle was estimated. If diffusion occurs much faster than the droplet’s flight time in the nozzle, the solvent vapor is expected to fully diffuse, resulting in a vapor density away from the droplet approximated as Equation 6 below considering the 1:2 ratio of carrier to sheath gas flows and presumed saturation within the carrier gas.

[0153] Equation 61' p V, CO = ~P v, s

[0154] If the diffusion timescale is much longer than the droplet’s flight time in the nozzle, the sheath gas may remain devoid of solvent vapor, thereby yielding a vapor density away from the droplet approximated as pv r~ 0. Different assumptions of pv rcan affect solvent evaporation time calculations, influencing the maximum aerosol size capable of gelling before reaching the substrate and thus altering the predicted morphology of AJ-printed surfaces.

[0155] The diffusion coefficient of THF vapor was estimated based on the known oxygen diffusion coefficient (0.176 cm2 / s) and the Stokes-Einstein equation as shown in Equation 7 below:

[0156] Equation 7where kBis the Boltzmann constant, T is the temperature, / is the dynamic viscosity, and R is the radius of the diffusing droplets. With Equation 8 below:

[0157] Equation 81D °c —]Rthe diffusion coefficient of THF vapor was calculated to be 0.170 cm2 / s using the oxygen diffusion coefficient, the dynamic viscosities of oxygen and THF vapor, and the molecular radii of oxygen and THF.

[0158] The diffusion timescale was then estimated by Equation 9 below:

[0159] Equation 9r2T“ 2Dwhere r is the characteristic diffusion length scale.

[0160] For the two regions of the nozzle (Region I and Region II, depicted in FIG. 3 A), the characteristic lengths are 375 pm and 75 pm, representing the respective radii of each region. The calculated diffusion timescales for these regions are 4.14x10' s and 0.17x10' s, while 3 3the droplet’s flight times are 5.44x 10' s and 0.09x 10' s, respectively, for Region I and Region II. Given the comparable timescales for diffusion and droplet flight within the two regions of the nozzle, we estimated solvent evaporation under the extreme scenarios of Equation 10 or Equation 11, which resulted in similar qualitative results discussed above.

[0161] Equation 101P V, = ~P

[0162] Equation 11p V, = 0

[0163] DS-PDMS Volume Fraction <bDS. PDMSas a Function of Time

[0164] According to Equation 1, the droplet evaporation rate depends on the size of the droplet size. Therefore, a small timestep dt = 1 x 10' s is used to calculate the amount of evaporated solvent, which dictates the volume change dv of the droplet and the new droplet radius Ra. For a droplet with an initial radius of ’"lltialin a solvent with a density ofsolvent, the volume change within a timestep can be calculated by Equation 12:

[0165] Equation 12

[0166] The droplet radius can be updated as Equation 13:

[0167] Equation 13

[0168] The DS-PDMS volume fraction after this timestep is according to Equation 14:

[0169] Equation 14

[0170] The calculation is looped until the droplet reaches gelation when <bDS. PDMS>is p1lotted as a function of time as illustrated in FIGs. 3B- 3D.

[0171] Various aspects of the invention include, but are not limited to, the aspects listed in the following numbered clauses.

[0172] Clause 1. A method for forming a superhydrophobic coating, the method comprising: aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas; directing the mist to a substrate, wherein the mist traverses to the substrate over a flight time; decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles; and contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate, wherein the superhydrophobic coating comprises the gel particles.

[0173] Clause 2. The method of clause 1, wherein decreasing the damping factor of the droplets within the mist during the flight time comprises removing at least a portion of the solvent from the droplets by evaporation during the flight time to increase a concentration of the polymer within the droplets.

[0174] Clause 3. The method of clause 2, wherein removing the solvent from the droplets by evaporation increases the concentration of the polymer by at least 0.1 volume fraction.

[0175] Clause 4. The method of any of clauses 2-3, wherein the solution comprises a first concentration of the polymer and the droplets comprise a second concentration of the polymer after solvent evaporation, wherein the second concentration is greater than the first concentration.

[0176] Clause 5. The method of clause 4, wherein the first concentration is no greater than 0.62 volume fraction.

[0177] Clause 6. The method of clause 4, wherein the first concentration is no greater than 0.5 volume fraction.

[0178] Clause 7. The method of any of clauses 4-6, wherein the second concentration is at least 0.62 volume fraction.

[0179] Clause 8. The method of any of clauses 1-7, wherein a drop-cast film prepared from the solution exhibits a contact angle of at least 70 degrees.

[0180] Clause 9. The method of any of clauses 1-8, wherein a drop-cast film prepared from the solution exhibits a contact angle of at least 90 degrees.

[0181] Clause 10. The method of any of clauses 1-9, wherein the polymer comprises at least one of a siloxane polymer, a thermoplastic polyurethane, a polyvinyl alcohol, a nylon, a sucrose, a cellulose, a protein, a polyethyleneimine, a polypropylene, and a polyethylene.

[0182] Clause 11. The method of any of clauses 1-10, wherein the polymer comprises polydimethylsiloxane.

[0183] Clause 12. The method of any of clauses 1-11, wherein the polymer comprises disulfide-polydimethylsiloxane.

[0184] Clause 13. The method of any of clauses 1-12, wherein the droplets comprise a diameter in a range of 100 nm to 50 pm.

[0185] Clause 14. The method of any of clauses 1-13, wherein the droplets comprise a diameter in a range of 100 nm to 10 pm.

[0186] Clause 15. The method of any of clauses 1-14, wherein the droplets comprise a diameter in a range of 100 nm to 1 pm.

[0187] Clause 16. The method of any of clauses 1-15, wherein the superhydrophobic coating exhibits a contact angle of at least 150 degrees.

[0188] Clause 17. The method of any of clauses 1-16, wherein the superhydrophobic coating exhibits a contact angle of at least 160 degrees.

[0189] Clause 18. The method of any of clauses 1-17, wherein the superhydrophobic coating exhibits a sliding angle of no greater than 10 degrees.

[0190] Clause 19. The method of any of clauses 1-18, wherein the superhydrophobic coating exhibits a surface roughness of at least 0.5 pm.

[0191] Clause 20. The method of any of clauses 1-19, wherein the solvent comprises an organic solvent.

[0192] Clause 21. The method of any of clauses 1-20, wherein the solvent comprises a polar solvent.

[0193] Clause 22. The method of any of clauses 1-21, wherein the solvent comprises a polar aprotic solvent.

[0194] Clause 23. The method of any of clauses 1-22, wherein the solvent comprises at least one solvent selected from the group consisting of tetrahydrofuran, dimethylformamide, and N-Methyl-2-pyrrolidone, chloroform, methanol, ethanol, acetone, dimethyl sulfoxide (DMSO), acetonitrile, and ethyl acetate.

[0195]

[0196] Clause 24. The method of any of clauses 1-23, wherein the solvent is miscible with the polymer.

[0197] Clause 25. The method of any of clauses 1-24, wherein the solvent comprises a vapor pressure of at least 0.1 mmHg.

[0198] Clause 26. The method of any of clauses 1-25, wherein the solvent comprises a vapor pressure of at least 100 mmHg.

[0199] Clause 27. The method of any of clauses 1-26, wherein the gel particles do not coalesce upon deposition.

[0200] Clause 28. The method of any of clauses 1-27, wherein the method is an additive manufacturing method.

[0201] Clause 29. The method of clause 28, wherein the additive manufacturing method comprises aerosol jetting.

[0202] Clause 30. The method of clause 29, wherein the superhydrophobic coating is patternable with dimensions of 25 microns or greater.

[0203] Clause 31. The method of any of clauses 1-30, wherein the gas comprises nitrogen.

[0204] Clause 32. The method of any of clauses 1-31, wherein the gas comprises air.

[0205] Clause 33. The method of any of clauses 1-32, wherein the flight time is no greater than 1 second.

[0206] Clause 34. The method of any of clauses 1-33, further comprising: directing the mist and / or gel particles towards the substrate utilizing a nozzle.

[0207] Clause 35. The method of clause 34, further comprising introducing a sheath gas into the nozzle.

[0208] Clause 36. The method of clause 35, further comprising focusing the mist and / or gel particles within the sheath gas within the nozzle to form a collimated stream of mist.

[0209] Clause 37. The method of any of clauses 1-36, wherein the superhydrophobic coating comprises a network of interconnected gel particles.

[0210] Clause 38. The method of any of clauses 1-38, wherein decreasing the damping factor of the droplets within the mist during the flight time comprises polymerizing the polymer.

[0211] Clause 39. The method of clause 38, wherein polymerizing the polymer comprises exposing the droplets to ultraviolet electromagnetic radiation.

[0212] Clause 40. An article produced by the method of any of clauses 1-39, wherein the article comprises the substrate and the superhydrophobic coating.

[0213] Clause 41. The article of clause 40, wherein the superhydrophobic coating covers less than all of the surface area of the substrate.

[0214] Clause 42. An additive manufacturing system configured to perform the method of any of clauses 1-39.

[0215] Clause 43. A method for forming a superhydrophobic coating, the method comprising: aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas; directing the mist to a substrate, wherein the mist traverses to the substrate over a flight time; gelling the droplets, thereby forming gel particles; and contacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate, wherein the superhydrophobic coating comprises the gel particles.

[0216] Any patent, publication, or other disclosure material identified herein is incorporated herein by reference in its entirety unless otherwise indicated but only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material expressly set forth in this specification. As such, and to the extent necessary, the express disclosure as set forth in this specification supersedes any conflicting material incorporated by reference herein. Any material, or portion thereof, that is said to be incorporated by reference into this specification, but which conflicts with existing definitions, statements, or other disclosure material set forth herein, is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.Applicant reserves the right to amend this specification to expressly recite any subject matter, or portion thereof, incorporated by reference herein.

[0217] In this specification, unless otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about,” in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described herein should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0218] Also, any numerical range recited herein includes all sub-ranges subsumed within the recited range. For example, a range of “1 to 10” includes all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited. All such ranges are inherently described in this specification.

[0219] Any references herein to “various examples”, “some examples”, “one example”, “an example”, or like phrases mean that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment. Thus, appearances of the phrases “in various examples”, “in some examples”, “in one example”, “in an example”, or like phrases in the specification do not necessarily refer to the same examle. Furthermore, the particular described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation. Such modifications and variations are intended to be included within the scope of the present embodiments.

[0220] As used herein, “at least one of’ A and B, means only A, only B, or both A and B. Additionally, there may be multiple As and / or multiple Bs.

[0221] One skilled in the art will recognize that the herein described articles and methods, and the discussion accompanying them, are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated. Consequently, as used herein, the specific examples / embodiments set forth and the accompanying discussions are intended to be representative of their more general classes. In general, use of any specific exemplar is intended to be representative of its class, and the non-inclusion of specific components, devices, operations / actions, and objects should not be taken to be limiting. While the present disclosure provides descriptions of various specific aspects for the purpose of illustrating various aspects of the present disclosure and / or its potential applications, it is understood that variations and modifications will occur to those skilled in the art.Accordingly, the invention or inventions described herein should be understood to be at least as broad as they are claimed and not as more narrowly defined by particular illustrative aspects provided herein.

Claims

CLAIMSWhat is claimed is:

1. A method for forming a superhydrophobic coating, the method comprising:aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas;directing the mist to a substrate, wherein the mist traverses to the substrate over a flight time;decreasing a damping factor of the droplets within the mist during the flight time, thereby forming gel particles; andcontacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate, wherein the superhydrophobic coating comprises the gel particles.

2. The method of claim 1, wherein decreasing the damping factor of the droplets within the mist during the flight time comprises removing at least a portion of the solvent from the droplets by evaporation during the flight time to increase a concentration of the polymer within the droplets.

3. The method of claim 2, wherein removing the solvent from the droplets by evaporation increases the concentration of the polymer by at least 0.1 volume fraction.

4. The method of claim 2, wherein the solution comprises a first concentration of the polymer and the droplets comprise a second concentration of the polymer after solvent evaporation, wherein the second concentration is greater than the first concentration.

5. The method of claim 4, wherein the first concentration is no greater than 0.62 volume fraction.

6. The method of claim 4, wherein the first concentration is no greater than 0.5 volume fraction.

7. The method of claim 4, wherein the second concentration is at least 0.62 volume fraction.

8. The method of claim 1, wherein a drop-cast film prepared from the solution exhibits a contact angle of at least 70 degrees with water.

9. The method of claim 1, wherein a drop-cast film prepared from the solution exhibits a contact angle of at least 90 degrees with water.

10. The method of claim 1, wherein the polymer comprises at least one of a siloxane polymer, a thermoplastic polyurethane, a polyvinyl alcohol, a nylon, a sucrose, a cellulose, a protein, a polyethyleneimine, a polypropylene, and a polyethylene.

11. The method of claim 1, wherein the polymer comprises poly dimethylsiloxane.

12. The method of claim 1, wherein the polymer comprises disulfidepoly dimethylsiloxane.

13. The method of claim 1, wherein the droplets comprise a diameter in a range of 100 nm to 50 pm.

14. The method of claim 1, wherein the droplets comprise a diameter in a range of 100 nm to 10 pm.

15. The method of claim 1, wherein the droplets comprise a diameter in a range of 100 nm to 1 pm.

16. The method of claim 1, wherein the superhydrophobic coating exhibits a contact angle of at least 150 degrees with water.

17. The method of claim 1, wherein the superhydrophobic coating exhibits a contact angle of at least 160 degrees with water.

18. The method of claim 1, wherein the superhydrophobic coating exhibits a sliding angle of no greater than 10 degrees.

19. The method of claim 1, wherein the superhydrophobic coating exhibits a surface roughness of at least 0.5 pm.

20. The method of claim 1, wherein the solvent comprises an organic solvent.

21. The method of claim 1, wherein the solvent comprises a polar solvent.

22. The method of claim 1, wherein the solvent comprises a polar aprotic solvent.

23. The method of claim 1, wherein the solvent comprises at least one solvent selected from the group consisting of tetrahydrofuran, dimethylformamide, N-Methyl-2-pyrrolidone, chloroform, methanol, ethanol, acetone, dimethyl sulfoxide, acetonitrile, and ethyl acetate.

24. The method of claim 1, wherein the solvent is miscible with the polymer.

25. The method of claim 1, wherein the solvent comprises a vapor pressure of at least 0.1 mmHg.

26. The method of claim 1, wherein the solvent comprises a vapor pressure of at least 100 mmHg.

27. The method of claim 1, wherein the gel particles do not coalesce upon deposition.

28. The method of claim 1, wherein the method is an additive manufacturing method.

29. The method of claim 28, wherein the additive manufacturing method comprises aerosol jetting.

30. The method of claim 29, wherein the superhydrophobic coating is patternable with dimensions of 25 microns or greater.

31. The method of claim 1, wherein the gas comprises nitrogen.

32. The method of claim 1, wherein the gas comprises air.

33. The method of claim 1, wherein the flight time is no greater than 1 second.

34. The method of claim 1, further comprising:directing the mist and / or gel particles towards the substrate utilizing a nozzle.

35. The method of claim 34, further comprising introducing a sheath gas into the nozzle.

36. The method of claim 35, further comprising focusing the mist and / or gel particles within the sheath gas within the nozzle to form a collimated stream of mist.

37. The method of claim 1, wherein the superhydrophobic coating comprises a network of interconnected gel particles.

38. The method of claim 1, wherein decreasing the damping factor of the droplets within the mist during the flight time comprises polymerizing the polymer.

39. The method of claim 38, wherein polymerizing the polymer comprises exposing the droplets to ultraviolet electromagnetic radiation.

40. An article produced by the method of claim 1, wherein the article comprises the substrate and the superhydrophobic coating.

41. The article of claim 40, wherein the superhydrophobic coating covers less than all of the surface area of the substrate.

42. An additive manufacturing system configured to perform the method of claim 1.

43. A method for forming a superhydrophobic coating, the method comprising:aerosolizing a solution comprising a polymer and a solvent, thereby producing a mist comprising droplets of the solution entrained in a gas;directing the mist to a substrate, wherein the mist traverses to the substrate over a flight time;gelling the droplets, thereby forming gel particles; andcontacting the gel particles with the substrate, thereby forming the superhydrophobic coating on the substrate, wherein the superhydrophobic coating comprises the gel particles.

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