Spray‐Coating of Superhydrophobic Coatings for Advanced Applications

Superhydrophobic coatings are widely applicable, e.g., as self‐cleaning surfaces or water–oil separation membranes, yet their wider usage is impeded due to costs of fabrication, size, or substrate limitation. Spray‐coating is a versatile coating procedures and might offer a good solution for the fabrication of these superhydrophobic coatings, due to the fact that coatings can be fabricated on various materials in a simple, fast, and inexpensive manner. Most procedures rely on hybrid coatings of hydrophobized nanoparticles and a polymeric matrix, which have several drawbacks including the easy loss of nanoparticles and difficult waste handling. Here, the fabrication of the superhydrophobic material, called Fluoropor, for the first time, by spray‐coating on various substrates including metals, tissues, concrete, and glass is presented. It is fabricated by spray‐coating a mixture of a highly fluorinated monomer blended with porogens followed by photopolymerization. The superhydrophobicity of the material relies on the porous structure on the micro‐/nanoscale across the bulk material and does not require any nanoparticles. Excellent self‐cleaning ability of these coatings, resistance against thermal and abrasive impact, and their application as oil–water separation membranes are shown. This versatile applicability is highly promising for real‐world application as self‐cleaning coatings or oil–water separating membranes.


Introduction
Superhydrophobic materials find wide application such as self-cleaning surfaces, [1][2][3][4][5][6][7] oil-water separating membranes, [1,3,8,9] or as protective coatings [5,10] in a multitude of fields. Superhydrophobic surfaces are defined as surfaces that exhibit static water contact angles (WCAs) above 150°and rolloff angles (ROAs) lower than 10°. [11] This high repellence relies on the combination of a low surface energy material and a surface structure that can maintain the water droplet in the so-called Cassie-Baxter (CB) state, where the droplet rests on top of the asperities of the surface structure, entrapping a thin layer of air underneath. [12] Such superhydrophobic surfaces can be fabricated artificially by techniques like anodization, [13] etching, [14][15][16][17] hot embossing, [18] and lithographical processes. [17] However, these superhydrophobic surfaces often require expensive and multistep fabrication techniques, [16,17,19] are limited to a certain class of substrate material [13][14][15][16][17][18] or facilitate the coating of only small surface areas . [14,15,17] They also often require post-functionalization with a low surface energy material. [15][16][17] Therefore, all these techniques impede the fabrication of superhydrophobic surfaces when it comes to obtaining large superhydrophobic surface areas. Spray-coating is a versatile technique that has the advantage to be capable of coating large surface areas in a simple, scalable, fast, and inexpensive manner on a variety of materials. [20] Hence, many strategies have been developed to fabricate superhydrophobic surfaces by spray-coating over the past decades. Most of these approaches involve the usage of particles, e.g., silica, [2,5,8,10,[21][22][23][24][25][26][27][28][29][30][31][32][33][34] fumed alumina [35] or titanium dioxide [4] nanoparticles, halloysite nanotubes , [36] carbon nanotubes [37] or polytetrafluoroethylene. [38] The addition of these particles is crucial to obtain coatings with a structure on the micro-/nanoscale, which is one of the requirements to maintain the liquid, i.e., water, in the superhydrophobic CB state. In contrast, a low surface energy material is required that surrounds the particles and renders them hydrophobic. Common reagents include fluoro-/alkylsilanes on silica nanoparticles, [8,21,22,24,[27][28][29]31,33,34] polydimethylsiloxane, [10,23,25] or similar low surface energy polymers such as Silres, [2] an emulsion of alkoxyl silanes and fluoropolymer, custom-synthesized polymers based on sulfur, diisopropylbenzene, and fluoroalkene, [5] fluorinated polybenzoxazine [30] or Capstone, [32] a water-based acrylic fluorochemical dispersion. However, all these nanocomposite materials show drawbacks such as, e.g., the necessity of the additional hydrophilization step with fluoro-/alkylsilane, which requires large amounts of chemicals due to the high surface area of the nanoparticles, the risks related to handling nanoparticles [39][40][41][42][43][44] which require additional safety measures as well as the difficult waste handling and emission commonly encountered with nanocomposites. [45] Therefore, fully polymeric self-structuring spray coatings promise an attractive approach for the fabrication of superhydrophobic surfaces. Sometimes the inherent structure of a surface can be used to achieve special wetting properties, e.g., on mesh structures, or fabrics. As an example, spray-coating a polyhedral oligomeric silsesquioxane (POSS) hybrid methacrylate copolymer solution on steel meshes showed good oilwater separation properties [46] and the mist polymerization of lauryl methacrylate on cotton fabrics achieves super-repellence. [47] Yet both of these approaches are limited to the shown substrates, i.e., steel mesh, and cotton fibers, as the microstructure of these substrates is required for the superhydrophobicity of these coatings. Approaches based on layer-by-layer deposition of spray-coated polymers to obtain a micro-/nanorough surface structure, which was subsequently spray-coated with a perfluoro alkyl silane and a perfluoro alkyl sulfuric salt has been demonstrated as well. [48] Although these surfaces exhibited superhydrophobic behavior, the necessity of performing 80 spraying cycles impedes the application as a coating procedure for wider practical use. Alternatively, waxes can be used to fabricate superhydrophobic coatings via spraying from an ethanol solution. [49,50] Yet, these coatings usually suffer from poor abrasion resistance and lose their superhydrophobicity above around 80°C once the wax starts melting.
In this article, we present the spray-coating of a micro-/ nanoporous fluoropolymer foam onto a wide variety of materials including metals, glass, and microfiber tissue resulting in superhydrophobic surface properties. This approach is based on Fluoropor, a material previously developed by our group, [51,52] for which we developed a spray-coating procedure. We show that these coatings can maintain their repellence under thermal treatment, and abrasion. Moreover, we show that the coating possesses excellent self-cleaning ability as well as for the manufacturing of oil-water separating membranes and oil-skimming materials.

Fabrication of Fluoropor Spray-Coating Solution
Micro-/nanoporous fluoropolymer foam coatings were fabricated using the previously reported Fluoropor solutions. [51] In brief, the bifunctional methacrylate monomer MD700 with a fluorination degree of 52 wt% was blended with 1 H,1 H,2 H,2 H-Perfluorooctan-1-ol (13FOOl), and cyclohexanol, the porogens, and the initiator DMPAP, which was presolved in acetone (1 mg μL À1 ). The mixture was 50 wt% of MD700 with 35 wt% 13FOOl, and 15 wt% cyclohexanol for Fluoropor15 or 25 wt% of 13FOOl, and 25 wt% cyclohexanol for Fluoropor25 (the number after the term Fluoropor indicates the amount of added cyclohexanol in wt%). Finally, the initiator DMPAP was added at a concentration of 1 wt% of the monomer.

Preparation of Coating Substrates
Different substrates were functionalized prior to spray-coating to ensure proper adhesion of the Fluoropor coating. Glass slides were cleaned and activated in a first step by dipping in a 50:50 v v À1 solution of methanol and hydrochloric acid followed by rinsing with isopropanol and water. In a second step, the glass slides were dip-coated in a 0.1 M solution of MACS in dry toluene followed by a rinse with isopropanol and water. For the metal substrates, such as aluminum and steel, a commercially available functionalization solution from Aculon was utilized. After an initial cleaning of the substrates with an acetone-soaked paper towel, the substrates were cleaned in the Aculon Cleaner 905 solution diluted with water (1:4 v v À1 ) at 40°C for 5 min with ultrasonic agitation. The substrates were rinsed with water and dried with nitrogen gas prior to dip coating in the Aculon Methacrylate Functional Adhesion Promoter solution for 5 min. Finally, excessive solution was removed from the substrate surface with a paper towel. The microfiber tissue was washed in acetone and dried in the fume hood before spray-coating. The concrete sample was fabricated by mixing 26 g NaOH, 45 mL water, and 100 g of Eco2cem powder and curing for 24 h. The sample was washed in water to remove excessive NaOH from the surface and was used without any further functionalization.

Spray-Coating of Substrates
The substrates were placed inside a nitrogen-filled chamber and spray-coated with a SATAjet 4000 B RP spray gun from SATA (Germany) utilizing nitrogen gas with a pressure of 0.8 bar. Then the sprayed coating was polymerized utilizing a Hellas UV exposure unit from Bungard (Germany) for 5 min and rinsed in acetone to remove the uncured top layer from the coating. Next, the coatings were washed in isopropanol overnight to remove the porogens from the material followed by drying. Finally, the coating surface was opened with sandpaper (grid 2000) to remove the closed lid layer from the bulk-porous material, which forms upon the drying procedure.

Characterization
The repellence was characterized by an OCA 15EC contact angle goniometer from DataPhysics (Germany) and evaluated with SCA20 software. Static water contact angles and roll-off angles were measured with 5 μL sized water droplets with a tilting speed of 1.24°s À1 . The surface structure of the Fluoropor surfaces was characterized by scanning electron microscopy (SEM) on a Quanta 250 FEG device from FIE Inc. (USA) with an accelerating potential of 5 kV. The samples were placed on SEM sample holders and sputtered with a circa 26 nm thick layer of gold palladium. The adhesion of the Fluoropor coatings to the substrates was analyzed by a normed cross-hatch test with the Cross Cut Adhesion Test Kit CC 1000 from TQC (Netherlands). UV/VIS-spectra were measured with an Evolution 201 UV/VIS-spectrometer from Thermos Scientific (Germany). Fourier transformed infrared spectroscopy (FTIR) measurements were conducted on a Frontier FTIR spectrometer from Perkin Elmer (USA). Spray-coated Fluoropor surfaces were measured utilizing the Universal ATR Sampling accessory unit for the spectra from 4000 to 600 cm À1 and analyzed by the enclosed Spectrum software. X-ray photoelectron spectroscopy (XPS) was conducted on a PHI 5000 VersaProbe III (USA) spectrometer to analyze the atomic composition.

Temperature Stability
Thermal stability of the repellence of Fluoropor was investigated by heating the Fluoropor coating in a Vacu-Therm VT6025 furnace from Thermo Scientific (Germany) to 100°C for 1 h. The wetting behavior of the Fluoropor coating was assessed before and after this treatment.

Abrasion Persistence of Wetting Behavior
The influence of abrasion on the repellence of Fluoropor coatings was assessed by measuring the wetting behavior before and after abrasion. Additionally, the surface structure was characterized by SEM imaging. Abrasion of the surface was performed with sandpaper (grid 2000), which was loaded with 200 g and moved for 200 cycles over the surface manually.

Self-Cleaning Ability Test
To assess the self-cleaning ability of the spray-coated Fluoropor surfaces artificial particles were used as contaminants. For quantitative testing, spray-coated Fluoropor25 surfaces on glass slides were contaminated with 4.16 mg cm À2 of silicon carbide (400 mesh and 37 μm size, SiC). Subsequently, the surfaces were tilted by 18°and washed with water droplets (47.2 μL cm À2 ) to remove the contaminants. The degree of contamination was assessed by photographical images, which were evaluated by ImageJ software using a thresholding algorithm: In a first step, the images were cropped and transformed into 8-bit images. Next, the threshold function was applied to detect all dark particle spots from the contaminate and measured the fraction of surface area covered by these. Additionally, the repellence of the surface before and after contamination was compared to evaluate whether particles changed the surface properties. The experiment was performed on three different samples. Besides, self-cleaning was also shown qualitatively for sea sand, methylene blue, Sudan black and Sudan red G on Fluoropor15 and Fluoropor25 spray-coated glass slides (videos of self-cleaning included in Supporting Information).

Oil-Skimming and Oil-Water Separation
For oil-skimming experiments chloroform dyed with Sudan red G was added to a vial with water. A piece of a microfiber tissue (1 Â 1 cm) spray-coated with Fluoropor25 was cut and submerged in this mixture until it was in contact with the chloroform droplet. After skimming the chloroform droplet in water, the soaked tissue was removed from the vial. Results were observed by a camera (see video in Supporting Information).
For oil-water separation, crude oil and water were mixed. A circular Fluoropor membrane with a diameter of 5 cm was cut from a Fluoropor25-coated microfiber tissue and placed inside a customized filtering device which consisted of a funnel, a metal filter plate with pores, and a fixation clip. The oil-water mixture was then poured onto the Fluoropor membrane and vacuum was applied shortly for 3 s applied to the vacuum flask. Subsequently, the vacuum was removed and the penetrating water was collected in the vacuum flask. The separation efficiency (η) was calculated based on the following equation where m water, after and m water, before refer to the mass of the water after and before separation, respectively.

Results and Discussion
Fluoropor is a fluoropolymer foam with a porous structure on the micro-/nanoscale throughout the bulk of the material. [51] In this work, we were able to show for the first time the fabrication and application of Fluoropor as large area surfaces via spray-coating. In brief, for Fluoropor the bifunctional methacrylate-based monomer MD700 is blended with a mixture of the two porogens, i.e., cyclohexanol, which is immiscible with MD700, and 13FOOl, which is miscible with MD700. This mixture forms a thermodynamically stable single-phase solution. During photoinitiated free radical polymerization, the increasing molecular weight of the forming polymer causes the mixture to reach a point where the mixture is thermodynamically unstable and a phase separation of the porogens from the polymer sets in.
www.advancedsciencenews.com www.aem-journal.com This phase separation occurs over the spinodal decomposition mechanism until the forming polymer reaches its gelation point and the phase separation is stopped. [53] This phenomenon is called polymerization-induced phase separation. [54,55] After the removal of the porogens from the polymer by washing and drying, a porous polymer network is obtained. The superhydrophobicity of Fluoropor relies on the combination of a low surface free energy material (i.e., a fluoropolymer with a high fluorination degree) and the rough surface structuring which results from the intrinsic porosity induced via the porogen. The pore size of the polymer foam can be adjusted by altering the porogen composition, i.e., the higher the amount of the immiscible cyclohexanol the broader the pore size distribution towards larger pores of the foam. Liquid Fluoropor formulations were spraycoated in a nitrogen-enriched atmosphere using a commercial paint spray-gun and cured with UV light on various substrates, such as steel, aluminum, glass, concrete, and microfiber tissues as shown in Figure 1a-i. In addition, larger areas such as, e.g.,20 Â 20 cm 2 sized steel panels (see Figure 1e) could be easily spray-coated. Coatings were manufactured using two Fluoropor variants with slightly different porogen compositions, i.e., Fluoropor15 (see Figure 1a,c,f ), and Fluoropor25 (see Figure 1b,d,e,g,h,i). Both Fluoropor variants were spray-coated to generate coatings with different pore sizes and thus different properties. While Fluoropor15 coatings with smaller pores are still translucent (see Figure 1f and S1, Supporting Informatoin) being advantageous for applications where transparency is required, Fluoropor25 with larger pores is white and shows a slightly enhanced repellence. [52,56] The different optical appearance of Fluoropor15 and Fluoropor25 is caused by light scattering at the air/material interface of the pores of the material: while the pores of Fluoropor15 are below the light www.advancedsciencenews.com www.aem-journal.com scattering threshold of visible light [51] the pores of Fluoropor25 are larger causing light scattering in visible wavelength resulting in a whitish appearance of this material. During the washing and drying step, an unstructured closed lid formed on top of Fluoropor which was removed by abrasion with sandpaper. The thus revealed porous structure of Fluoropor is able to maintain water in the superhydrophobic C-B wetting state with a WCA of 163 AE 2°, 165 AE 2°and ROA of 8 AE 3°, 6 AE 2°f or Fluoropor15 and Fluoropor25, respectively (see Figure 2a,b). The coatings were also characterized by FTIR and XPS measurements to characterize the chemical composition of the surface. The FTIR spectra showed for Fluoropor15 and Fluoropor25 the characteristic peaks of perfluoropolyethers, such as MD700 (see Figure S2, Supporting Information). [57] Additionally, the chemical composition was characterized by XPS for Fluoropor15 and Fluoropor25 showing a high degree of fluorine on the surface (see Table S1, Supporting Information). To illustrate the high repellence toward water, dyed water droplets are shown on a Fluoropor15 coating sprayed on an aluminum substrate (see Figure 2c). Besides the high repellence, the coatings are also required to show good adhesion toward the substrates which is a requirement for a robust coating in practical applications. Therefore, the adhesion of the fabricated coatings was examined by a normed cross-hatch cutting test. [58] The Fluoropor15 coating on aluminum was tested to be class 0 and the Fluoropor15 coating on steel to be class 1, the highest and second highest category out of 6 categories, respectively (see Figure 2d,e). Also, for all other substrates and for Fluoropor25, these tests were conducted (see Table S2, Supporting Information). The adhesion ranges between class 0 for Fluoropor15 on glass or aluminum and the still moderate adhesion class 3 for unfunctionalized concrete with Fluoropor25, showing that the coating does not necessarily require functionalization steps before spray-coating. In conclusion, the adhesion of Fluoropor to the prefunctionalized substrates is very good to excellent making these coatings promising for wider application.
For real-world applications, superhydrophobic spray-coatings are required to maintain their repellence when heating as this occurs naturally under environmental conditions. To this end, we tested the repellence of Fluoropor coatings before and after heating to 100°C for 1 h. It was found that the WCA changed only insignificantly as a consequence of this treatment. For Fluoropor15, the initial WCA was 162 AE 1°before and 163 AE 1°after heating while the WCA was slightly higher for Fluoropor25 with 165 AE 1°before and 165 AE 1°after heating (see Figure 3a). Also, there was no significant change in the ROA from 7 AE 3°to 8 AE 4°for Fluoropor15 and from 6 AE 1°to 7 AE 3°for Fluoropor25, respectively. Moreover, SEM micrographical images proved that the micro-/nanoporous surface structure of Fluoropor15 and Fluoropor25 did not change upon heating and the surfaces maintained their high repellence (see Figure 3a). In summary, the spray-coated Fluoropor surfaces retained their high repellence performance even after heating to 100°C. Besides thermal impact, a real-world superhydrophobic coating must be insensitive to abrasive impact, i.e., retaining its superhydrophobicity upon abrasion. To test this, Fluoropor coatings were abraded for 200 cycles with a 200 g weighted sandpaper and the repellence was compared before and after abrasion treatment. It was found that the high repellence of the Fluoropor coatings persisted upon abrasive impact. The WCA changed insignificantly from 163 AE 1°to 161 AE 2°and from 165 AE 1°to 163 AE 3°for Fluoropor15 and Fluoropor25, respectively (see Figure 3b). Also, the change of the ROA was found to change insignificantly, from 9 AE 3°to 7 AE 2°and 6 AE 2°to 6 AE 2°for Fluoropor15 and Fluoropor25, respectively. The persistence of the wetting behavior relies on the porous structure of Fluoropor which is present throughout the bulk material. When abrasion occurs and the topmost structured layer is removed, a new structured layer is revealed. This was shown by SEM micrographical images of the surface structure showing the presence of the porous topography before and after abrasion (see Figure 3b). Fluoropor is thus superior to spray-coated superhydrophobic surfaces, which rely on incorporating nanoparticles in thin layers as these coatings lose their superhydrophobic properties upon abrasion. [59] Fluoropor will maintain its repellence as long as the residual coating is left on the substrate. In conclusion, spray-coated Fluoropor retains its high repellence upon abrasive impact.
One major advantage of superhydrophobic surfaces for real-life application is their self-cleaning ability, i.e., the effect that repelled water droplets roll off the surface capturing solid particles from the surface and thus removing them. Spray-coated Fluoropor surfaces were examined for their self-cleaning ability, on the one hand, quantitatively using silicon carbide (SiC) analogously to our previous work [56] and, on the other hand, qualitatively with inorganic (sea sand) and organic particles (Methylene blue, Sudan Black and Sudan Red G). For the quantitative testing, Fluoropor25 spray-coatings were chosen, because their white appearance allows a good estimation of the contaminated area by image analysis due to the high contrast between the bright surface and the dark SiC particles. Photographs of the coatings were taken before contamination, after contamination with SiC, and finally after the surface was self-cleaned with water (see Figure 4a). The photographs were analyzed with ImageJ to estimate the contaminated area for each stage of the experiment (see Figure S4, Supporting Information). Before contamination with SiC particles, the surface showed 0.014 AE 0.005% of the contaminated area which is a result of the storage condition in the laboratory atmosphere (see Figure 4b). After contamination, the contaminated area increased significantly to 52.670 AE 3.263% as www.advancedsciencenews.com www.aem-journal.com the dark SiC particles on the surface were deposited. After selfcleaning, the contaminated area is reduced to 0.022 AE 0.009% which is insignificantly differing from the initial value. Besides, the wetting behavior before contamination and after self-cleaning was assessed showing that the repellence did not differ significantly. The WCA changed insignificantly from 166 AE 2°to 165 AE 2°and the ROA from 7 AE 2°to 6 AE 2°. The surface was also able to self-clean when being submerged in water showing that all particles were removed upon lifting from the water (see Figure S5 and Video S11, Supporting Information). In conclusion, the Fluoropor surfaces showed the ability to be selfcleaned of all contaminate particles without influencing the repellence. The coatings' self-cleaning ability was shown qualitatively for different dye particles on spray-coated Fluoropor15 and Fluoropor25 surfaces. For all particles on all surfaces complete self-cleaning was observed. Representatively in Figure 4c,d,e,f self-cleaning is shown for Fluoropor15 and Fluoropor25 with Methylene blue and Sudan Red G (videos for each particle and surface pair can be found in the Supporting Information). Besides application as self-cleaning surfaces, spray-coated Fluoropor can find application in oil-water separation. For this, Fluoropor25 was spray-coated on microfiber tissues which we refer to as Fluoropor membrane. First, oil-water skimming was tested by immersion of a Fluoropor membrane inside a vial filled with water and dyed chloroform at the bottom (see Figure 5a). Upon immersion in water, a silvery shining air layer formed on the surface of the Fluoropor membrane, the so-called Salvinia layer. [60,61] As soon as the membrane reaches the organic phase, the chloroform is soaked into the Fluoropor membrane resulting in the complete removal of the chloroform phase within a few seconds (a video of the oil-skimming can be found in the , Supporting Information). This oil-skimming behavior can be explained by the selective wettability of the Fluoropor membrane, where chloroform is capable of entering the pores and filling them due to its lower surface tension. Chloroform is here in the so-called Wenzel wetting regime, where a liquid completely wets the solid surface. [62] While water cannot penetrate or wet the membrane, the organic liquid is able to wet the membrane due to its lower surface tension. As a consequence, Fluoropor membranes are able to selectively remove immiscible organic liquids from water as long as they are able to wet the membrane, i.e., have a sufficiently low surface tension. Moreover, Fluoropor membranes were tested as filtration membranes to remove crude oil from water. For this, circular Fluoropor membranes with a diameter of 5 cm were cut from the coated tissue and placed on a customized filtration funnel with a large pores metal sieve. The whole setup was mounted with a clip and placed on top of a vacuum flask (see Figure 5b). Then a crude oil-water mixture Figure 4. Self-cleaning ability of Fluoropor. a) For quantitative analysis of the self-cleaning ability, Fluoropor25 surfaces on glass slides were first contaminated with SiC and self-cleaned in a second step by water droplets rolling off the surface. Image analysis of the contaminated area revealed that the surfaces were cleaned completely leaving no significant contamination back. b) The repellence of the Fluoropor spray-coating did not change before and after self-cleaning. Successful self-cleaning on: c,d) Fluoropor15 and e,f ) Fluorpor25 shown qualitatively with: c,e) Methylene blue and d,f ) Sudan red G as contaminants (I: before self-cleaning, II: after self-cleaning). The translucent Fluoropor15 coatings appear white due to the angle under which the images were taken and the illumination. Scale bar: 2 cm. www.advancedsciencenews.com www.aem-journal.com was poured onto the membrane. Initially, all of the liquid stayed above the membrane as the water-repellent membrane did not allow the water to penetrate. The vacuum flask was then vacuumed shortly (around 3 s) water started dripping into the flask immediately. The vacuum could then be removed and the oilwater separation continued driven by gravitational forces. After the separation, the membrane was soaked with the crude oil showing that it could successfully filter and store it (a video of the oil-water separation can be found in the , Supporting Information). The separation efficiency (η) was calculated based on the water that was separated from the oil (see Equation (1)). For this, the water was weighed before and after separation, and the separation efficiency was calculated to be 93.0 AE 0.3% (the values used for the calculation are in the Table S3, Supporting Information). These results show that nearly all water could have been separated from the oil-water mixture demonstrating the potential for Fluoropor membranes to be applied in oil-water separation applications. In summary, the successful separation of organic liquids, namely chloroform and crude oil, from water was accomplished by using Fluoropor membranes as oil-skimming material or as filtration membranes showing the material´s high potential in this field of application.

Conclusion
In this work, large-area superhydrophobic surfaces were successfully fabricated by spray-coating on multiple different substrates and tested for their potential for real-world applications. Fluoropor, a highly repellent fluoropolymer foam, was fabricated from a mixture of the fluorinated monomer MD700 blended with two porogens, which was applied on different substrates such as metals, glass, tissues, and concrete by spray-coating. During polymerization, the porogens phase separates from the polymer which are washed out with isopropanol leaving back a bulkporous foam. Surfaces of up to 20 Â 20 cm 2 were successfully coated and showed good adhesion of Fluoropor as well as superhydrophobicity of the surfaces. The fabricated coating showed stability of the repellence over thermal treatment of up to 100°C and for 200 abrasive cycles with a 200 g weighted Figure 5. Oil-water separation with Fluoropor25 coated microfiber tissue (referred to as Fluoropor membrane). a) Chloroform (red) was successfully removed by skimming with a Fluoropor membrane from water within seconds. b) Crude oil was removed from water by filtration through a Fluoropor membrane. The oil-water mixture was poured onto the membrane mounted in a customized laboratory filtration setup (I). After initial vacuuming of the membrane (II), the separation continues just by gravitational forces (III). The oil-water mixture on the membrane (IV) was separated leaving back the crude oil-soaked membrane (V). Scale bar: 2 cm.
www.advancedsciencenews.com www.aem-journal.com sandpaper. This is due to the porous structure of Fluoropor which is present throughout the bulk volume. Moreover, the self-cleaning ability of Fluoropor was examined quantitatively and qualitatively for different kinds of contaminate particles showing high self-cleaning performance of the coatings. Lastly, Fluoropor spray-coated microfiber tissues were used successfully in oil-water separation by skimming of chloroform from water and by filtration of crude oil from water with a separation efficiency of 93%. In summary, the ability to spray-coat Fluoropor on different substrates combined with its high stability to temperature and abrasion make this promising for application as spray-coatings for real-world applications. Future work will focus on the industrial scalable application of Fluoropor coatings.

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.