Research Article pubs.acs.org/journal/ascecg
Development of Dual-Phobic Surfaces: Superamphiphobicity in Air and Oleophobicity Underwater Bichitra N. Sahoo,† Naga Siva Kumar Gunda,† Sonil Nanda,‡ Janusz A. Kozinski,‡ and Sushanta K. Mitra*,† †
Micro & Nano-scale Transport Laboratory, Lassonde School of Engineering, and ‡Department of Earth and Space Science and Engineering, Lassonde School of Engineering, York University, Toronto M3J1P3, Canada ABSTRACT: In the present work, we describe a simple method to fabricate dual-phobic fluorosilane-coated polydimethylsiloxane/camphor-soot/polydimethylsiloxane (FPCP) composite surfaces. The surface morphology and silane treatment provide the needed texture on the FPCP composite surface to demonstrate superamphiphobicity in the air and oleophobicity in the underwater environment. High-resolution field emission-scanning electron microscopy (FESEM) imaging of the FPCP composite surface illustrates the top surface with an array of hollow cylindrical pillars. The dimensions of surface texture are measured, and the relationship between the wetting states of liquid and textures surface in the air as well as in an underwater environment is studied. Also, X-ray photoelectron spectroscopy (XPS) analysis demonstrates different changes of plain polydimethylsiloxane (PDMS), PDMS/camphor-soot/PDMS (PCP), and fluorosilane-coated PCP (FPCP) composite surfaces that are responsible for diverse wettability properties. We compared the experimentally observed equilibrium and dynamics contact angles of water and different oils on the FPCP composite surface in air and underwater system with those predicted by theoretical models. The results reported herein provide a new feasible method for the fabrication of dual-phobic surfaces (superamphiphobicity in air and oleophobicity underwater) with microtextures. The findings also improve the understanding of the complex relations between surface microstructure and wetting states. The fundamental understanding of dual-phobicity of FPCP composites is an important step toward the designing of optimal anti-icing surfaces for practical engineering applications. Such coatings with incorporated functionalities provide promising self-cleaning and anticorrosion applications under erosive/abrasive environment. KEYWORDS: PDMS, Contact angle, Fabrication, XPS, FESEM, Silane, Composite surface, AFM
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surface curvatures11−13 have been found useful for achieving superoleophobicity. However, the fabrication of those structures is usually limited to particular substrates and relies on sophisticated process control. Moreover, the superoleophobicity of those nature-inspired surfaces (e.g., lotus leaf effect)14 can be only maintained in surrounding air medium.15 Studies related to the unique wettability phenomena in nature have become important for scientific research to advance the design of functional interfacial materials.16,17 Recently, the discovery of underwater self-cleaning fish skin inspired us to develop a new way to fabricate superoleophobic surfaces.18 This novel strategy takes advantage of the water-favoring property of high-energy materials to achieve surprising oil repellency in an oil/water/solid three-phase system.19,20 Recently, oil-repellent materials, especially those with an underwater superoleophobicity, have attracted wide attention for their promising applications in antifouling coating,21−23 oil/water separa-
INTRODUCTION Alteration of the surface wettability through chemical and/or physical modifications has attracted considerable attention for a broad spectrum of applications such as antifogging, selfcleaning coatings, microfluidic devices, liquid−liquid separation membrane, etc. Superhydrophilic and superhydrophobic coatings that demonstrate extreme wetting behaviors have been pursued for in-depth research in recent years.1−3 In contrast to superhydrophobic surfaces (which only repel water), superamphiphobic surfaces extend these extreme phobic properties to organic solvents and surfactant containing solutions, which have resulted in a much broader range of applications.4,5 However, the fabrication of superamphiphobic surfaces is still a major challenge in surface chemistry because the established methods to fabricate superhydrophobic surfaces are no longer sufficient, and an even more precise design of micro- to nanoscale hybrid structures is required.6 Superoleophobic surfaces (which repel oils) with highly repellent characteristics for low surface tension liquids (i.e., oils) are important to applications such as inkjet printing, antifouling of ship hulls, and antifinger print films.7,8 Several specific microstructures such as nanofilaments,9 overhang structures,10 and re-entrant © 2017 American Chemical Society
Received: March 30, 2017 Revised: June 30, 2017 Published: July 5, 2017 6716
DOI: 10.1021/acssuschemeng.7b00969 ACS Sustainable Chem. Eng. 2017, 5, 6716−6726
Research Article
ACS Sustainable Chemistry & Engineering
Figure 1. Schematic description for the fabrication of dual-phobicity PDMS/camphor-soot composite surface.
tion,24,25 metal cleaning,26,27 and small oil droplet manipulation.28 There is a real challenge in fabricating such underwater oleophobic surfaces.29 The oleophobic surfaces in the air usually show oleophilicity in underwater systems. The traditional method of creating oleophobic surfaces in the air depends on fluorinated treatments using the chemical vapor deposition. These surfaces are not stable for a longer time due to physical adsorption of the fluorinated groups. Hence, these surfaces tend to lose the fluorinated layers in underwater systems. Therefore, it is challenging to create efficient and multipurpose underwater surfaces. As a typical example, Liu et al.30 coated layers of graphene oxide (GO) on commercially available wire meshes to prepare underwater superoleophobic membranes. Similarly, Sun et al.31 fabricated hierarchical polydimethylsiloxane (PDMS) microstructures with extreme underwater superoleophobicity by combining O2 plasma modification and surface microstructures for the development of oleophobic microfluidic channels. Jin et al.32 have used a complex process involving grafting poly(acrylic acid) using a salt-induced phase-inversion approach to achieve superhydrophilic and underwater superoleophobic poly(vinylidene difluoride) filtration membranes. Also, fabrication of superamphiphobic surface in air with underwater oleophobic characteristics is indeed rare.33 Often complex micro- and nanoarray structures are used to achieve underwater superoleophobic characteristics.34−40 These limited and complicated studies warrant the development of a facile, low-cost, and scalable method for fabricating superoleophobic surfaces that can be easily applied to any target object and maintain surface wettability under repeated external harsh conditions. More importantly, it needs to work both in air and underwater. In addition, underwater wettability produces an additional scientific challenge such as the role of trapped water layer remains unclear in controlling the underwater oleophobic characteristics of oil droplets on such surfaces.18,41 Therefore, it is of great interest to fabricate the underwater oleophobic surfaces with superamphiphobicity in air to study the trapped water phase, if any, within such structures. In this work, we have developed dual-phobic fluorosilane-coated polydimethylsiloxane/camphor-soot/polydimethylsiloxane (FPCP) composite surfaces, which exhibit superamphiphobicity in air and oleophobicity underwater. These dual-phobic surfaces were prepared on a glass substrate by successively coating a layer of
polydimethylsiloxane (PDMS) followed by camphor-soot and again PDMS. In simple words, camphor-soot layer is sandwiched between two layers of PDMS. The top surface of this composite layer is treated with oxygen plasma followed by treatment with 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) by a simple dipping method. A novel self-cleaning ability of PDMS/camphor-soot particles polymer composite with self-healing ability to self-repair from chemical (nitric acid etching) and mechanical damages (sand grains) is developed. The polymer composite has the optimal loading of the camphor-soot particles, which reveals a water contact angle of 171°.42,43 The developed dual-phobic surfaces were characterized using field emission-scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Furthermore, the wetting behavior of these dual-phobic surfaces is performed using contact angle measurements with water and various kinds of oil in surrounding air medium as well as in underwater system. The wetting study showcased that the dual-phobic surfaces developed in this work have excellent superamphiphobicity in air and oleophobicity underwater. Furthermore, the experimental results are corroborated with theoretical models. The fundamental understanding of dual-phobicity of FPCP composites is a crucial step toward the designing of optimal anti-icing surfaces for practical engineering applications.44 Such coatings with incorporated functionalities provide promising self-cleaning and anticorrosion applications under erosive/ abrasive environment.45 In the present study, we have fabricated the dual-phobic FPCP surfaces using PDMS and camphor-soot particles. The fabrication method is simple and developed in the lab without depending on the sophisticated nanofabrication facilities, which are expensive to use. The simplicity and low-cost in the fabrication of present dual-phobic surfaces will allow long-term sustainability. In addition, the materials such as PDMS and camphor-soot particles are easily available at low-cost, and they have minimal environmental impact, and are thereby a promising sustainable alternative to traditional corrosive chemicals used for anti-icing/superhydrophobic coatings.
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EXPERIMENTAL SECTION
Materials. All chemicals used in this work were of analytical grade without further treatment. Camphor (96%), ethanol (reagent grade), acetone (HPLC phase > 99.9%), tetrahydrofuran (THF, anhydrous, 99.9%), nitric acid (70% concentration), 1H,1H,2H,2H-perfluorooctyl6717
DOI: 10.1021/acssuschemeng.7b00969 ACS Sustainable Chem. Eng. 2017, 5, 6716−6726
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ACS Sustainable Chemistry & Engineering
Figure 2. FESEM image of (a) three-layer coating of PDMS/camphor-soot composite surface on glass surface composite (scale bar 100 μm). (b) FESEM image of camphor-soot particles (scale bar 10 μm). (c) Plain PDMS coating (scale bar 100 μm). (d) FESEM image of superhydrophobic PDMS composite surface (inset image reveals the optical images of the water droplet with a volume of 5 μL on superhydrophobic PDMS composite surface) (scale bar 100 μm). (e) Photographic image showing the high CAs of a water droplet on the superhydrophobic surface in air. triethoxysilane (POTS, 98%), glycerol (99.5%), ethylene glycol (99.6%), n-hexadecane (99%), and tetradecane (99%) were purchased from Sigma-Aldrich, U.S. Polydimethylsiloxane (PDMS, Sylgard 184 Silicone Elastomer Kit with components of PDMS base and curing agent) was obtained from Dow Corning Ltd., Canada. SYLGARD 184 Silicone Elastomer Kit comprised of siloxane monomer base and curing agent was mixed in a base-to-curing agent ratio of 10:1 by weight to form the PDMS solution. PDMS was cured by an organometallic cross-linking reaction. The curing agent had a patented platinum-based catalyst that catalyzed the addition of the SiH bond across the vinyl groups of siloxane monomer base to form Si−CH2− CH2−Si cross-linkages.43 Microscopic glass slides (75 × 25 × 2 mm, Fisher Scientific, Canada) were used as the substrate material for the coating process. Camphor tablets of 5 × 5 × 2 mm size were used as the source materials for the generation of carbon soot particles.43 A spray gun (1.5 mm diameter nozzle size with operating pressure >40 psi and working pressure >10 psi) was purchased from the local market to produce necessary coatings on the substrates. Fabrication of Fluorosilane-Coated PDMS/Camphor-Soot/ PDMS (FPCP) Composite Surface. Here, we describe the fabrication of fluorosilane-coated PDMS/camphor-soot/PDMS (FPCP) composite surface on a glass substrate. Figure 1 depicts the schematic representation of FPCP fabrication process. The glass substrates with required dimensions were ultrasonicated (Bransonic ultrasonic bath, model 5800H, Branson Ultrasonics Corp., Danbury, CT) at 40 kHz in 20 mL of ethanol/water for 30 min followed by deionized water for 5 min. The PDMS solution then was formed by mixing 0.2 g of PDMS and 0.02 g of the corresponding curing agent in 30 mL of THF using a magnetic stirrer for 45 min at ambient temperature (23 °C). Next, the prepared PDMS solution was spray coated on the glass substrate. During the spraying process, the gap between the glass substrate and spray gun nozzle was maintained at a distance of 100−150 mm. The duration of spraying was 30 s, and the process was carried out five times for each sample to obtain a thin homogeneous coating. The PDMS-coated glass substrates were cured at 80 °C for 3 h to get the stable hydrophobic surfaces. In the next step, these cured PDMS substrates were placed above the camphor flame for 20−30 s, which led to the formation of a thick layer of camphor-soot particles on the PDMS surface. The distance between the sample surface and flame was maintained at 50 mm. The PDMS solution was sprayed on camphor-soot particles-coated PDMS surfaces. Once again, these PDMS/camphor-soot composite films were cured at 80 °C for 3 h. The developed PDMS/camphor-soot/ PDMS (PCP) composite surface exhibited superhydrophobicity in air. The prepared PCP composite surfaces were subjected to O2 plasma treatment to modify the surface chemistry. The O2 plasma treatment was conducted with a plasma cleaner (Haric Plasma, PDC-001-HP (115 V); PDC-002-HP (230 V)) at 110 Pa and 30 W for about 30 s.
The O2 treatment changed the PCP composite surface into superhydrophilic surface. In the next step, a fluorosilane solution was prepared to convert the superhydrophilic surface to a superoleophobic one. This fluorosilane solution preparation starts with making an ethanol solution by adding about 10 mL of deionized water to 80 mL of ethanol. An appropriate amount of acetic acid then was added to the ethanol solution to adjust its pH value to 3. An amount of 3 mL of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS) was then added into the acidic ethanol solution and stirred for 30 min at ambient temperature to obtain a fluorosilane solution. The O2 plasma treated PCP composite surfaces were immersed in the fluorosilane solution for 72 h. The coated samples then were placed on a hot plate at 80 °C for 1 h. It should be noted that the FPCP surfaces created in this work were not formed by physical adsorption of fluorosilane on the PCP surface using chemical vapor deposition.46 The fluorosilane was coated with dip treatment method after O2 plasma treatment. Hence, the fluorosilane created a covalent bonding with PCP surface, which was durable and strong even for a longer time and under harsh conditions. Further studies are needed for the comprehensive understanding of the durability of these developed surfaces. As demonstrated in Figure 1 and later through contact angle measurements, the FPCP composite surfaces prepared here had dual-phobicity, that is, superamphiphobicity in air and oleophobicity underwater. To understand the effects of silane treatment on surface wettability, the plain glass slide was also subjected to O2 plasma treatment followed by fluorosilane treatment. We have also performed water wettability studies for the plain glass surface, O2 plasma treated glass, and fluorosilane treated glass surface. Material Characterization. The morphology of FPCP composite surfaces was characterized by field emission-scanning electron microscopy (FESEM) (Quanta 3D FEG, FEI, Hillsboro, OR). X-ray photoelectron spectroscopy (XPS) measurements on FPCP composite surfaces were carried out using a Thermo Scientific K-Alpha XPS spectrophotometer (East Grinstead, UK) to detect the presence of surface elements. Thermo Avantage software (version 5.9) was used to perform curve fitting and to calculate the atomic concentrations. Atomic force microscopy (AFM) analysis was carried out on FPCP composite surfaces using an Agilent 4500 AFM microscope (Agilent Technologies Ltd., CA) operating in an intermittent contact mode. Measurement of Static and Dynamic Contact Angles. Measurement of sessile drop contact angles and the dynamic contact angles (advancing and receding) of water and different oils on FPCP composite surfaces was conducted in an air medium and an underwater system using a custom-made contact angle measurement instrument at the Micro and Nanoscale Transport Laboratory in the Lassonde School of Engineering.47 The commonly used technique such as tangent angle at three-phase contact points on a sessile drop profile was used to measure the contact angle. Holmarc contact angle 6718
DOI: 10.1021/acssuschemeng.7b00969 ACS Sustainable Chem. Eng. 2017, 5, 6716−6726
Research Article
ACS Sustainable Chemistry & Engineering software (Holmarc Opto-Mechatronics Pvt Ltd., Kochi, Kerala, India) was used to extract the contact angle values. The static contact angle was recorded by dispensing a water droplet (5 μL volume) on the fabricated surface. The advancing and the receding contact angles were measured by increasing and decreasing the drop volume, respectively. Each contact angle was an average of the measurements taken at five various locations on the same sample.
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RESULTS AND DISCUSSION Characterization of PDMS/Camphor-Soot/PDMS (PCP) Composite Surface. Figure 2 shows the FESEM images of the PDMS/camphor-soot/PDMS (PCP) composite surface. Figure 2a shows the cross-section of PCP composite surface. It is clearly observed that PCP composite was comprised of camphor-soot layer sandwiched between two thin layers of PDMS. Figure 2b and c illustrates the exploded FESEM image of camphor-soot particles and PDMS (bottom layer), respectively. It is found that the PDMS layer was smooth and uniform, whereas the camphor-soot layer looked uneven with slight roughness. Figure 2d shows the top view of the FESEM image of the PCP composite surface. The composite surface was created during the curing process of PDMS layer at 80 °C wherein the soot particles were adsorbed into the PDMS polymer. The top PDMS layer was transformed into a hollow cylindrical PCP composite surface via intramolecular rearrangement, which eventually underwent polymerization.48,49 It is believed that a strong interaction between the THF and soot particles had occurred that led to this polymerization. The sintering process was responsible for the developed surface texture of PCP composite film. During the curing process, there were likely synergistic effects between the reactive groups of PDMS (Si−OH and Si−O−CH3) and camphor-soot particles (−OH) groups. When the heating approached curing temperature, the PCP composite structure was gradually formed, making the structure denser. Meanwhile, the surface particles disappeared and generated regular hollow cylindrical structures. Therefore, as shown in Figure 2d, the PCP composite film after heating to 80 °C for 2−3 h illustrates the hollow cylindrical pillar structures. The inset image in Figure 2d reveals the superhydrophobicity of PCP composite with a static contact angle of 160°. Figure 2e shows the optical image of water droplets placed on the PCP composite surface. Characterization of Fluorosilane-Coated PDMS/Camphor-Soot/PDMS (FPCP) Composite Surface. The PCP composite surface rendered the micro structures with the possibility of surface modification. A two-way process to convert the superhydrophobic PCP composite surface to superamphiphobic FPCP composite surface was applied to the PCP composite surface. First, the PCP composite surface was completely converted to a superhydrophilic surface by using O2 plasma etching process, as described earlier in Figure 1. Because of the introduction of numerous hydroxyl groups on PDMS composite surface, the surface was thoroughly wetted by water. As shown in Figure 3a, the FESEM image of O2 plasma treated PCP composite surface illustrates the micro structures. Second, the O2 plasma treated PCP composite surface was immersed in POTS solution for 72 h to form FPCP composite surface. With the presence of a hydroxyl group, fluoroalkyl groups were grafted with silanol groups onto the micro structure via intermolecular condensation. By heating at 80 °C for 3 h, the surface recuperates micro structures with regular arrays of hollow cylindrical pillars. During fluorination
Figure 3. (a) FESEM image of the oxygen plasma treated PDMS composite surface (scale bar 100 μm). (b) FESEM image of superamphiphobic PDMS composite surface (Scale bar 100 μm). (c) Zoomed-in section of FESEM image of a POTS modified PDMS composite surface and its simplistic structures as a hollow cylinder (scale bar 10 μm). (d) Top view of the PDMS composite surface illustrating the square arrangement of surface features (scale bar 10 μm). AFM image of the oxygen plasma treated PDMS composite surface: (e) 2D, (f) 3D. AFM image of superamphiphobic PDMS composite surface: (g) 2D, (h) 3D.
treatment, a low surface tension shielding layer with fluoroalkyl groups was formed on the outside of the micro structure. As shown in Figure 3b, FPCP composite surface illustrates well-organized arrays of hollow cylindrical structures. Figure 3c and d shows the exploded view of the microstructure on FPCP composite surface from the top and side, respectively. To further probe the wetting characteristics, AFM measurements were performed on a 2.5 μm × 2.5 μm scan area of the surface for both O2 plasma treated PCP and perfluoroalkyl silanemodified PCP (i.e., FPCP) composite surfaces to quantify the nanometric roughness. The average roughness and root-meansquare roughness (RMS) of the composite surfaces were taken as an average of the measurement at three different positions on the surface. As shown in Figure 3e, the average roughness and RMS of PCP composite surface upon O2 plasma etching were 255.59 and 267.32 nm, respectively. The corresponding 3D AFM of the O2 plasma treated PCP composite surface is illustrated in Figure 3f. Furthermore, 2D and 3D AFM measurements of the PCP composite surface upon fluoroalkyl silane modification (i.e., the resultant FPCP composite surface) are illustrated in Figure 3g and h, respectively. It was found that 6719
DOI: 10.1021/acssuschemeng.7b00969 ACS Sustainable Chem. Eng. 2017, 5, 6716−6726
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ACS Sustainable Chemistry & Engineering
Figure 4. (a) Photographic images of water, ethylene glycol, glycerol, hexadecane, and tetradecane on the as-prepared superamphiphobic. (b) Optical images of the water droplet on (i) plain glass slide, (ii) oxygen plasma treated glass slide, and (iii) fluorine treated glass slide. (c) XPS spectra results of the as-fabricated surfaces of PDMS, PDMS/camphor-soot composite, oxygen plasma treated PDMS composite surface, and fluoroalkyl treated PDMS composite surface. (d) High-resolution C 1s spectrum.
To quantify the chemical changes of the elements comprising the composite surface, we have performed an XPS analysis at each step toward the fabrication of the desired FPCP composite surface, that is, plain PDMS surface, PCP composite surface, O2 plasma treated PCP composite surface, and FPCP composite surface (Figure 4c). The C 1s (284.6 eV), O 1s (532.5 eV), and Si 2p (102.7 eV) peaks were detected on the surface of the plain PDMS, PCP composite, and O2 plasma treated PCP composites.50 However, for fluorinated PCP (i.e., FPCP) composite surface, the C 1s is exhibited at the binding energy of 292.1 eV. It was observed that the percentage of C, O, and Si atoms for plain PDMS and PCP composite samples were 43.99, 28.57, and 27.20, respectively. Upon O2 plasma etching of PCP composite, the percentage of O2 atoms increased to 34.6. Furthermore, it was seen that upon POTS treatment of O2 plasma treated PCP composite surface (i.e., FPCP), the total content of fluorine atoms on the surfaces was 43.13 and the percentage of oxygen atom relatively reduced to 13.31. The deposited fluoroalkyl groups are observed via a significantly strong F 1s peak that appeared at 689.3 eV in the XPS spectrum of fluorinated PDMS composites. As shown in Figure 4d, the image demonstrates the high-resolution C 1s peaks of the FPCP composite surface.51−53 The spectra were deconvoluted into six component peaks with binding energy characteristics of the molecular units comprising the polymer
the average roughness and RMS roughness of FPCP composite surface were 273.27 and 283.19 nm, respectively. Upon O2 plasma treatment of PCP composite surface, the surface was induced with a hydroxyl group and damaged, which led to superhydrophilicity with a contact angle of zero degrees. As shown in Figure 3g, the surface illustrates clusters, lumps, and island-like morphologies as compared to that of the O2 plasma treated PCP composite surface. By comparing Figure 3e and f, one can conclude that the surface coating of PCP composites surface upon fluorine treatment exhibits closer particle packing than that of the superhydrophilic PCP composite surface. As shown in Figure 4a, both plain glass substrate and O2 plasma treated surface demonstrated hydrophilicity with a water contact angle around 25°. Moreover, when a water droplet was placed on fluorine-silane treated glass surface, the surface exhibited hydrophobicity with a water contact angle of 109 ± 4°. The higher hydrophobicity is ascribed to the introduction of fluoroalkyl groups on the glass surface. Therefore, it is apparent that a simple silane and fluorine treatment cannot achieve the desired superamphiphobicity as obtained for our fabricated FPCP composite surface. On the other hand, the excellent superamphiphobicity for our fabricated composite surface was clearly reflected in the nearly spherical profiles and shape of liquid droplets deposited on the composite surface (Figure 4b). 6720
DOI: 10.1021/acssuschemeng.7b00969 ACS Sustainable Chem. Eng. 2017, 5, 6716−6726
Research Article
ACS Sustainable Chemistry & Engineering network, including −CC/C−H (284.2 eV), −C−O (285.7 eV), −CH2−CF2 (286.7 eV), −CO (289.3 eV), −CF2 (291.9 eV), and −CF3 (294.26 eV). The CF2/CF3 ratio closely resembled the value of five, which confirms that the interface is strongly affected with fluoroalkyl chains.54,55 It has been reported that the lowest surface energy groups in monolayer films have an order of −CH2− > −CH3 > −CF2− > −CF2H > −CF3.52 Thus, PFOA is suitable for lowering the surface energy due to its high content of −CF3, −CF2−, and the carboxyl groups.50 It is evident that the presence of CF3 groups is important and known to play a prominent role in lowering the surface free energy. Wettability of FPCP Composite Surface in Air. Figure 5a demonstrates the chemical nature of the FPCP composite
composite surface in the air medium. The liquid contact angles to the glycerol, ethylene glycol, n-hexadecane, and tetradecane were 159 ± 1°, 155 ± 3°, 145 ± 1°, and 141 ± 1°, respectively, as shown in Figure 5b and Table 1. Table 1. Surface Tension (mN/m) and Experimental Contact Angle Values (deg) for Water and Oil in Air on Different Substrates water and different oils in air
surface tension (mN/m)
glass slide (deg)
plain PDMS coating (deg)
PCP composite coating (deg)
FPCP coating (deg)
water glycerol ethylene glycol nhexadecane tetradecane
72 64.00 47.80
47 ± 1 76 ± 2 65 ± 1
115 ± 3 108 ± 3 95 ± 1
158 ± 3 142 ± 3 136 ± 2
165 ± 2 159 ± 1 155 ± 3
27.47
22 ± 3
45 ± 4
56 ± 2
145 ± 1
26.57
19 ± 3
40 ± 2
54 ± 3
141 ± 1
The advancing angle and the receding contact angles of water and other liquids on FPCP composite surface in the air medium are shown in Figure 5c. It is found that the contact angle hysteresis for water was around 10−15°. Meanwhile, as shown in Figure 5c, glycerol had average advancing and receding contact angles of 158 ± 1° and 148 ± 1°, respectively. Similarly, other liquids such as ethylene glycol, n-hexadecane, and tetradecane exhibit contact angle hysteresis
