Flexible and Stable Omniphobic Surfaces Based on Biomimetic

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Biological and Medical Applications of Materials and Interfaces

Flexible and Stable Omniphobic Surfaces based on Biomimetic Repulsive Air-Spring Structures Dongkwon Seo, Suk-kyong Cha, Gijung Kim, Hyunku Shin, Soonwoo Hong, Yang Hyun Cho, Honggu Chun, and Yeonho Choi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b20521 • Publication Date (Web): 16 Jan 2019 Downloaded from http://pubs.acs.org on January 17, 2019

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ACS Applied Materials & Interfaces

Flexible and Stable Omniphobic Surfaces based on Biomimetic Repulsive Air-Spring Structures Dongkwon Seo1, Suk-kyong Cha1, Gijung Kim1, Hyunku Shin1, Soonwoo Hong1, Yang Hyun Cho2, Honggu Chun1,3,*, and Yeonho Choi1,3,* 1Department

of Bio-convergence Engineering, Korea University, Seoul 02841, Republic of Korea,

2Department

of Thoracic and Cardiovascular Surgery, Samsung Medical Center, Seoul 06351,

Republic of Korea, 3School of Biomedical Engineering, Korea University, Seoul 02841, Republic of Korea Abstract In artificial biological circulation systems such as extracorporeal membrane oxygenation (ECMO), surface wettability is a critical factor in blood clotting problems. Therefore, to prevent blood from clotting, omniphobic surfaces are required to repel both hydrophilic and oleophilic liquids and reduce surface friction. However, most of omniphobic surfaces have been fabricated by combining chemical reagent coating and physical structures and/or using rigid materials such as silicon and metal. It is almost impossible for chemicals

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to be used in the omniphobic surface for biomedical devices due to durability and toxicity. Moreover, a flexible and stable omniphobic structure is difficult to be fabricated by using conventional rigid materials. This study demonstrates a flexible and stable omniphobic surface by mimicking the re-entrant structure of springtail’s skin. Our surface consists of a thin nanohole membrane on supporting microstructures. This structure traps air under the membrane, which can repel the liquid on the surface like a spring and increase the contact angle regardless of liquid type. By theoretical wetting model and simulation, we confirm that the omniphobic property is derived from air trapped in the structure. Also, our surface well maintains the omniphobicity under the highly pressurized condition. As a proof of our concept and one of the real applications, blood experiments are performed with our flat and curved surfaces and the results including contact angle, advancing/receding angles, and residuals show the significant omniphobicity. We hope that our omniphobic surface has a significant impact on blood-contacting biomedical applications.


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Keywords: omniphobic surface, re-entrant structure, blood-contacting, surface wettability, blood clotting.

Introduction

In biomedical devices such as extracorporeal membrane oxygenation (ECMO), the surface wettability is in great interest because it is directly related to adhesion and clotting problems of blood cells. Especially, clotting is related to the surface friction of blood and surface of blood-contacting parts. Surface friction of blood occur destruction of blood cells or platelets, so this destruction activates blood coagulation circuit and made clots. So, without anticoagulant drugs including heparin, these problems can cause blood flow to be blocked, which leads to hazardous circumstances or death. Accordingly, many researchers have tried to control the surface wettability of blood-contacting parts in the biomedical devices to repel the blood for reduction of the surface friction.1 To repel blood we need omniphobicity which has both hydrophobicity and oleophobicity because blood is a complex mixture of water, lipids, proteins, and blood cells. Therefore, to repel blood,


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at first, some structures in nature including lotus leaves, and bird feathers were mimicked for increasing hydrophobicity, but they showed lower oleophobicity than the flat surface, so they cannot have oleophobicity without additional chemical coatings.2-12 As Nepenthes’s lubricant repels oily fluids, chemical coatings such as perfluoro compounds are widely used.13-20 However, these chemicals are generally toxic and degrade over time. Therefore, it is not advisable to use chemical coatings directly for biomedical purposes and long-term processes.

Therefore, researchers turned their attention to fabricating omniphobic surfaces without using any chemicals. They found that the skin of an insect named springtail can repel both of aqueous and oily fluids. Their surfaces exhibit a micro-hoodoo structure, which is one of re-entrant structures.18-31 The re-entrant structure can block liquid permeation by trapping air between the structure and liquid.24,

27, 32-35

This leads to an increase in a

contact angle of the fluid on the re-entrant structure.34, 36-48 According to the Cassie-Baxter and Wenzel Models which are based on Young’s equation, air pockets help reduce the contact area so that it leads to a dramatic improvement in the contact angle. However,


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most omniphobic structures are convex.47-67 The convex structures have a challenge in resistance of pressure. In high-pressure condition, liquid push out the trapped air. Even when the pressure removed, the liquid remained the lower part of the structure, and their omniphobicity cannot be maintained. In addition, typical convex structures consist of ‘Tshape’, which are difficult to fabricate with flexible materials such as polydimethylsiloxane (PDMS). For this reason, they are typically composed of hard materials.47-57

In this paper, we fabricated a flexible and stable omniphobic surface by mimicking the re-entrant structure of springtail.21-22 Our surface can capture air under the structure, and trapped air acts like a spring which can prevent liquids from permeating (Figure 1a). So, our repulsive air-spring structure surface does not require any chemical coating but exhibited great performance to repel various liquids regardless of their surface tension (Figure 1b). Our repulsive air-spring structure is mimicking of springtail’s skin (Figure 1c). As shown in the cross-sectional SEM image, its nanostructure trapped air between the fluid and the structure by a re-entrant mechanism, repelling liquids. Therefore, we fabricated this structure by covering nanohole membrane on supporting microstructures


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(Figure 1d). Our surface showed an advanced omniphobicity against various liquids which have different physical properties. Moreover, our surface has resistance to the highpressure condition due to its concave structure. It also showed the significant stability for the mechanical deformation.68 Furthermore, we confirmed that our surface can be applied to a curved surface and their omniphobicity worked well in the blood-contacting condition.

Results and Discussion

Our surface consists of a 500 nm hole arrayed membrane and the micron-size pillar structures (Figure 1d). The micropillar array was composed of cubes (length: 10 μm, width: 10 μm and height: 10 μm) or cylinders (diameter:10 μm and height: 10 μm). The thickness of the nanohole membrane was 0.5 μm. For flexibility, we prepared the membrane and pillar structure using PDMS (Supporting Information Figure S1). The membrane is stably positioned on top of the micro-structures. We examined the mechanical stability of our surface by repeating bending. As a result, our surface can maintain its membrane until 75 times bending (Supporting Information Figure S2). Through holes in the membrane,


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we could identify the bottom part of the pillar structure. The air could be trapped between the nanohole membrane and the depressed engraving of the micro-pillar structure, repelling the liquid on the surface.

Our surface showed omniphobicity to liquids regardless of the surface tension. We measured contact angle of water and mineral oil (Figure 2). On a flat PDMS surface, water and mineral oil had the contact angle of 95 º and 54 º, respectively. On a nanohole surface alone, water and mineral oil represented the decreased contact angle contact angle of 52 º and 39 º, by the way on common micro-pillar structure, water showed an increased contact angle of 138 º, but the mineral oil showed a decreased contact angle of 27 º instead. On our surface, water showed increased contact angle of 151 º. Interestingly, the contact angle of the mineral oil dramatically increased to 112 º.

In order to theoretically confirm the changes in contact angle by the air-trapping, we used a finite element method for numerical analysis of the contact angle. Although the numerical analysis for a single re-entrant structure has been well proven, but the analysis about the variation of contact angles on the arrayed re-entrant structure has not been


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shown. Because of springtail’s skin shapes an arrayed nanohole, it was necessary to analyze the contact angle on the arrayed re-entrant structures, not on a single structure. For the reason, we built three different arrayed structures of a flat surface, pillar structures, and re-entrant T structures (Supporting Information Figure S3). Owing to the limitation of computational power, we simply constructed an arrayed T-structure model. Through this model, we have validated the theory efficiently. For water (surface tension = 72 mN / m) representing a liquid with high surface tension, the contact surface is found to be 95 °, 148 ° and 155 ° on flat surfaces, pillar structures and the re-entrant T-structure (Supporting Information Figure S3a). On the other hand, in the case of mineral oil (surface tension = 28 mN / m), which is a typical low surface energy liquid, the contact angle of pillar structure decreased from 50 º to 32 º as compared to the flat surface (Supporting Information Figure S3b). However, case of re-entrant structure, even if the fluid has a low surface tension, the fluid is pushed up by the trapped air and the contact angle increases to 147 °. This numerical analysis supported the omniphobic characteristics of our surface.


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So, we compared the contact angle changes in five liquids (water, glycerol, ethylene glycol, olive oil, and mineral oil) with the graphs of theoretically calculated for our repulsive air-spring structure using the Cassie-Baxter model and the Wenzel model (Supporting Information Figure S4). For calculation of each model, we basically used Young’s equation as follows:

Equation (1)

γSV ― 𝛾𝑆𝐿 = 𝛾cos 𝜃𝑌

here, γ refers to the surface tension at the liquid-gas interface, γSV and 𝛾𝑆𝐿 represent the surface tension at the solid-gas and liquid-solid interfaces, respectively, and 𝜃𝑌 is Young’s contact angle. However, since the actual contact surface is not ideally flat, the contact angle at the surface was calculated with the following equations: Equation (2)

cos 𝜃𝐶𝐵 = 𝑟𝑓𝑓cos 𝜃𝑌 + 𝑓 ―1

Equation (3)

cos 𝜃𝑊 = 𝑟cos 𝜃𝑌

where 𝜃𝐶𝐵 is the deformed contact angle, 𝑟𝑓 refers to the roughness ratio of the wet surface area, and 𝑓 is the fraction of surface area wetted by the liquid, when the Young’s contact angle of the liquid is greater than 90 º, the Cassie-Baxter model (Equation (2)).


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While, Young’s contact angle is less than 90 º; the Wenzel model (Equation (3)), 𝜃𝑊 is the contact angle of the liquid and 𝑟 is the ratio of the true contact area of solid surface to the apparent contact area.

According to these wetting models, all liquids on the flat and pillar surface were correlated with theoretical wetting models. However, on our repulsive air-spring structure surface, low surface tension liquids (ethylene glycol, olive oil, and mineral oil) changed their wetting model to the Cassie-Baxter model. Typically, the low surface tension liquids follow the Wenzel model, so they can permeate into the surface. This leads to increase of the contact area, reducing the contact angle. However, the repulsive air-spring structure can block the permeation of liquids, Then the low surface tension liquids followed Cassie-Baxter model on our surface. Accordingly, as the contact area decreased, the contact angle was increased. This suggests that our structure has the omniphobic property regardless of liquid types, compared to other common structures.

Moreover, we investigated changes in the contact angle by the hole-size in the membrane (Figure 3). We fabricated additional surfaces which have different hole-


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diameter: 0.5, 1.0, 1.5, and 2.0 μm. The nanohole membrane was fabricated by 1.0, 2.0, 3.0 and 4.0 μm PS bead. The PS beads were shrunk by O2 plasma to half of their original size. The subsequent process was same as basic fabrication procedures of original membrane. The contact angle of water decreased from 151 º to 118 º (Figure 3a) and that of mineral oil decreased from 112 º to 101 º (Figure 3b). Utilizing the numerical simulation, we identified that trapped air between the membrane and the depressed engraving of the micro-pillar structure contributed these changes. The simulation showed the distribution of air and liquid by the color map (Figure 3c, d). In the color map, the value of 1 (red) indicates the air-like domain and 0 (blue) is a liquid-like domain. We selected a domain which has 0.5 value as the interface between air and liquid. When water located on the surface, the surface which has 2.0 μm hole size keep less air in the structure, showing orange in the color map. However, the case of 0.5 μm hole size is filled with air, showing vivid red. In case of mineral oil, a relatively less air was trapped, comparing with water. However, the increase of trapped air with a decrease of hole-size was consistent. Furthermore, we estimated Cassie-Baxter wetting model which is correlated with the measured contact angle results. For this concept, we calculated the contact angle at the


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Cassie-Baxter model by considering the change of solid fraction (fs) when the liquid permeates into the inside of the hole, the bottom of the membrane, and the side of the micropillar (Supporting Information Figure S5). As the results, we theoretically confirmed that a contact angle similar to the experimental value obtained when the liquid permeated into the inside of the hole or the bottom of the membrane (Figure 3a, b). These results indicated that the decrease of hole-size led the increase of air-trapping and contact angle.

Moreover, our surface exhibited stable performance even after a pressure was given. We designed a situation which air flow give a high-pressure to the surface and liquid in a PDMS chamber (Supporting Information Figure S6). We observed the sunken-water were condensed inside the repulsive air-spring structure at 1.1 atm and 1.2 atm (Figure 4a). As the pressure increased, the water permeated through the membrane, but the sunkenwater pushed out the air when the pressure returned to 1.0 atm. Consequently, the surface maintained their repulsive air-spring structure even after pressure was given. We measured a contact angle changes to confirm restoration of omniphobicity. After the pressure was restored, the contact angles of the liquids remained the same as before


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(Figure 4b). These results showed our structure kept their omniphobicity even when the high-pressure was given. Furthermore, to examine the highest pressure that our surface can endure, we also observed more high-pressure situation from 1.5 to 2.0 atm (Supporting Information Figure S6). Our surface maintained the air-trapping effect until 1.7 atm. However, at 2.0 atm, the liquids permeated under the structure and the omniphobicity disappeared.

Meanwhile, for practical applications, the surface should maintain their omniphobicity in dynamic fluid movement. Thus, we investigated sliding contact angles of three type of liquids such as water, mineral oil, and blood (Figure 5). The water showed advancing angle of 166 º and receding angle of 142 º when the sliding angle was 16 º. The mineral oil showed advancing angle of 142 º and a receding angle of 100 º at 34 º. The blood showed advancing angle of 153 º and receding angle of 129 º at 21 º. Interestingly, the blood showed the advancing and the receding angle between those of water and mineral oil. Considering that the blood contains both of hydrophilic and oleophilic substance, this represent our surface exhibited reasonable omniphobic property.


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According to previous experiments, we tested our omniphobic surface with blood. The blood contact angle on the flat PDMS surface was 84 ° and blood droplets slowly flowed along the surface even when tilted for 45 º (Figure 6a). However, in the case of our surface with repulsive air-spring structure (Figure 6b), the contact angle of the blood increased by 56 º to the final standard of 140 º. When the surface tilted for 45 º, blood droplets flowed rapidly without residual substance (Supporting Information Movie S1). Moreover, we tried continually sliding three liquids, water, mineral oil, and blood, on our repulsive air spring structure, they slid very well(Supporting Information Movie S2). which means omniphobicity maintain at repeated flow condition. These results represented that our repulsive air spring structure meets the omniphobicity standards required on surfaces exposed to complex fluid mixtures and it maintained trapped air at a shape deformation or even in a continuous liquid flow.

Conclusion

In conclusion, we fabricated the intaglio repulsive air-spring surface showing omniphobicity that can repel blood, by combining the nanohole membrane and the


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micropillar array. Our surface can be fabricated with cost-effective and reproducible methods such as the nanosphere lithography and the photo-lithography. Our surface consisted of flexible materials such as PDMS. Thus, it could endure mechanical deformation after repetitive bending. On our surface, liquids showed increased contact angles regardless of their type. We examined these results by theoretical wetting model and identified that the wetting model of liquids was converted into the model elevating the contact angle. Through simulation, it was confirmed that the air trapped in the repulsive air-spring structure induced this change and decreasing of the hole-size improved omniphobicity by increasing air trapping effect. Also, due to the intaglio structure, our surface was stable under the pressurized condition. Liquids could permeate into the structure in high-pressure, but the trapped air pushed out the liquids after the pressure recovered. In addition, our surface maintained omniphobicity even when it tilted or curved, and the liquids slid down the surface rapidly. Consequently, our surface showed the advanced omniphobicity without any chemical treatment and also repelled blood without residual substances. Therefore, we expect our surface to be applied as a novel material for blood-contacting devices.


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Experimental Section

Fabrication of a Monolayer of Polystyrene Beads: A 4-inch wafer was thoroughly cleaned with a piranha solution (H2SO4:H2O2 = 3:1) for 30 min and rinsed using de-ionized water (DIW) and ethanol. A chromium (Cr) layer of 85 nm thickness was deposited on the wafer using an e-beam evaporator (Korea Vacuum Tech.). Meanwhile, a colloidal solution (1 mL) of 1, 2, 3, and 4 μm polystyrene (PS) beads was re-suspended in a water-ethanol (1:1) mixture using a centrifuge. Subsequently, using the Langmuir-Blodgett technique, a monolayer of the PS beads was formed on the Cr-deposited wafer. In order to shrink the PS beads to half size of origin bead size, the wafer was treated by O2 plasma (Femto Science, CUTE), where the plasma generation time was 8, 10, 12 and 13 min and the power, O2 flow rate, and pressure were 100 W, 2 sccm, and 4.5 x 10–2 torr, respectively.

Induced Coupled Plasma Reactive-ion Etching (ICP-RIE) for Si Pillar Structures: Cr layer was etched with ICP-RIE till silicon exposed. (Cl2 flow rate: 20 sccm, Ar flow rate: 10 sccm, ICP power: 900 W, plasma power: 100 W, treating time: 3 min 30 sec). When the silicon was exposed, the silicon was etched with ICP RIE until 1.5 μm height pillar is


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generated. (SF6 flow rate: 80 sccm, CH4 flow rate: 20 sccm, treating time: 2 min 30 sec). After ICP RIE process, PS sphere was removed with toluene (Daejung Chemicals & Metals) for 10 minutes then the chromium was etched with chromium etchant. The silicon nano pillar mold was coated with Tri-chloro (1H,1H,2H,2H-perfluoro-octyl) silane (SigmaAldrich) over 6 hours in vacuum chamber.

Fabrication of PDMS Membranes: 5 % polyvinyl alcohol (PVA, SAMCHUN) was poured on the petri dish cured in an oven under 80 ℃. The cured PVA film was peel off and attached on the quartz substrate. In order to attach the film perfectly, it is necessary to apply heat (about 80 ℃). PDMS was prepared with a 10:1 ratio and solved in toluene with 1:2 ratio. The PDMS-toluene solution was poured on the silicon nano-pillar mold and waited for until air bubble popping out. After the process, mold was spin-coated in 6500 RPM for 150 seconds and cured for 30 minutes on 100 ℃ hot plate. Then O2 plasma was treated on PDMS layer and PVA film. (Vacuum pressure: 600 mTorr, O2 flow rate: 100 sccm, Plasma generation power: 100 W, treating time: 1 minute 30 seconds). The PVA film and PDMS membrane were bonded on 95 ℃ hot plate for 30 minutes. When the


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bonding was done, PVA-PDMS membrane could be easily peeled off from the silicon mold.

Fabrication of Pillar Arrays of PDMS: A Positive photoresist (GXR-601, AZ Electronic Materials) was initially spin-coated on a Si wafer at 3000 rpm, which was then baked at 100 C. UV light was irradiated and for hard baking, the photoresist-deposited wafer was baked at 130 C. Later, it was developed using an AZ developer (AZ 300MIF, AZ Electric Materials). Next, we etched the Si wafer to 10 m height using a CF4-based deep reactive ion etching (DRIE, Plasma Therm Versaline) instrument. Oxygen plasma was used for clearing away the residual photoresist. Using the Si wafer as a substrate for micro-pillar arrays, we poured PDMS onto it and heated it at 70 C in an oven for one hour. After peeling off the PDMS layer, we could obtain an array of PDMS pillar structures.

Plasma Bonding Step: O2 plasma was treated on the PVA-PDMS membrane and PDMS micro-pillar array. (Vacuum pressure: 600 mTorr, O2 flow rate: 100 sccm, Plasma generation power: 100 W, treating time: 1 minute 30 seconds). The PVA-PDMS membrane and PDMS micro-pillar array was attached on 120 ℃ hot plate for 10 minutes.


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When the bonding was done, PVA film was dissolved in 80 ℃ water. This step will take about 1 hour to get rid of the PVA film totally.

Contact Angle Measurement: A single droplet (5 L) of mineral oil, olive oil, ethylene glycol (Daejung Chemicals & Metals), or glycerol (SAMCHUN) was dropped on the fabricated surfaces and the contact angles were measured by capturing digital photographs of the drops. In the same manner, a 5 L droplet of blood was dropped on a flat surface. In case of tilted state, we used 3D printed 45 º inclined surfaces. For sliding angle measurement, we used a protractor at the backside of surface and fixed it using a crank. In the case of the concave surface, the fabricated surface was attached to the inner concave side of a half-sectioned acrylic tube.

Stability Test for Pressure: Acrylic mold was prepared for PDMS chamber. A mixed PDMS monomer solution with curing agent into the acrylic mold and cured at 65 ℃. The cured PDMS chamber is separated from the acrylic mold. We then pierced a hole at the chamber by a hole punch to inject water and air into the chamber. After loading of the surface, opened chamber was enclosed using PDMS (Supporting Information Figure S6). Then, water was inpoured into the PDMS chamber through the hole for injection. After an


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enough water to cover the entire surface was filled, air was injected by using a valve control system. Each pressure steps, we took the chamber for 10 second to be stabilized. During this time, we observed the surface with a bright field microscope.

Stability Test for Mechanical deformation: We used syringe pump (Pump 11 Elite, Harvard Apparatus) to give same bending force to the surface. For stable test, we attached slide glass on moving part of syringe pump, and then we fixed the surface. We next set the software to repeat injection and withdraw mode with 37 mm/sec speed and 1.5 cm of reciprocation. We observed the surface after 0, 25, 50, 75, 100 and 125 times of repetition using the bright field microscopy.

Blood Preparation: Ten healthy males (age: 29  9 years; height: 178  4 cm; bodyweight: 85  11 kg; BMI: 26.8  3.7) between the ages of 18 and 50 years volunteered to participate in this study. This study was approved by the ethics committee of Korea University

Guro

Hospital,

and

written

informed

consent

was

obtained

from all participates in accordance with the Declaration of Helsinki. (Institutional review board no. KUGH13093-001).


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Contact Angle Simulation: A finite element method (FEM) tool, COMSOL Multiphysics (COMSOL Inc., Sweden) was used for contact angle simulation. We used a two-phase laminar flow module and the governing equations are as shown below: ∂𝑢

𝜌 ∂𝑡 +𝜌(𝑢 ∙ ∇)𝑢 = ∇ ∙ [ ―𝑝 ∙ 𝐼 + 𝜇(∇𝑢 + (∇𝑢)𝑇)] +𝜌 ∙ 𝑔 + 𝐹𝑠𝑡

Equation (4)

∇∙𝑢=0

Equation (5)

∂𝜙 ∂𝑡

(

∇𝜙

+𝑢 ∙ ∇𝜙 = 𝛾∇ ∙ 𝜖 ∙ ∇𝜙 ― 𝜙(1 ― 𝜙)|∇𝜙|

)

Equation (6)

where 𝜌 , 𝑢, 𝑝 , 𝐼, 𝜇, 𝑇, 𝑔 , and 𝐹𝑠𝑡 represent density, velocity, pressure, identity matrix, dynamic viscosity, temperature, gravity, and surface tension, respectively. In Equation 4, 𝜙 refers to the level set function; 𝜙 = 1 for air and 𝜙 = 0 for a liquid phase and its value is 0.5 for the interface between two fluids. 𝛾 and 𝜖 refer to the reinitialization parameter and thickness of the transition layer, respectively. We set a wetted wall as the boundary condition for our model. Under such conditions, flat surface, pillar structures, and re-entrant structures were designed as described in Supporting Information Figure S7. The volume of each loading liquid was 5 µL; the liquids used were water (surface tension: 72mN/m) and mineral oil (surface tension: 28 mN/m).


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The contact angles of water and oil insert results of contact angle on a flat PDMS surface (water: 95 º, mineral oil: 56 º). Other conditions are insert of room temperature (25 ℃) and atmosphere pressure (1 atm) simulation are pressure, condition for surface is ‘No slip’ condition. All the simulations are run on a Dell Precision T7600 with Xeon CPU E5−2630 2.30 GHz (6 processors) and 128 GB of memory. Details on the geometry and mesh setup can be found in the Supporting Information Figure S7 and S8.


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Figure 1. A repulsive air-spring based omniphobic surface that mimicked skin of springtail. (a) Schematic illustration of principle for repelling liquid on repulsive air-spring surface. (b) A repulsive air-spring surface repels liquids. Scale bar represents 1 cm. (c) Photograph of springtail and SEM image of re-entrant structure of springtail.34 SEM image is side topology of springtail’s skin. The scale bars represent 1 mm and 300 nm. Reproduced with permission from reference 34. Copyright 2013 American Chemical Society. (d) Photograph and SEM image at a tilted angle (60 º) for fabricated repulsive air-spring structure surface. The scale bars represent 1 cm, 10 μm, and 3 μm.


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Figure 2. A contact angle on four different structure surfaces (flat surface, 500 nm nanohole surface, 10 μm pillar structured surface, and our repulsive air spring surface). All surfaces consisted of PDMS. Side-view images of (a) water and (b) mineral oil droplet at three different surfaces. All scale bars represent 1 mm.


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Figure 3. Size of nanohole dependent contact angle changes by trapped air. (a-b) Changes of the contact angle of (a) water and (b) mineral oil by the nanohole size. The circle dots indicate experimental result of the contact angles and the black line represents trend line of contact angle by hole-size. The floating bars indicate the estimated range of the contact angle using corresponding wetting situation at the top of plotted data. (c-d) Simulation of air-trapping at (c) water and (d) mineral oil.


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Figure 4. The stability of our repulsive air-spring surface under pressure condition. (a) The bright field microscopy images of water on our surface at i) 1.0 atm, ii) 1.1 atm, iii) 1.2 atm and return to 1.0 atm. The red triangles indicate sunk-water into the nanohole membrane. All scale bars represent 50 μm. (b-c) The stable omniphobicity of our surface before and after pressure was given for (b) water and (c) mineral oil. All scale bars represent 2 mm.


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Figure 5. Sliding contact angle on our repulsive air-spring surface. θt represented the sliding angle of each liquids. Advancing and receding contact angle of (a) water, (b) mineral oil, and (c) human blood droplet. All scale bars represent 2 mm.


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Figure 6. Rapid sliding of blood on our repulsive air-spring surface without residual substance. (a) The blood sliding on the tilted surface. The tilted angle was 45 º. (b) The blood sliding on curved surface. In both of cases, blood rapidly slid along the surface within 0.1 sec. All scale bars represent 1 cm.


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ASSOCIATED CONTENT

Supporting Information.

The following files are available free of charge.

Solid fraction calculation, table of wetting ratio, fabrication of repulsive air-spring structures, mechanical stability test, simulation of contact angle, wetting model change on the repulsive air-spring structure, schematic image of wetting ratio, setup for pressure test and results of pressure stability limit, schematic diagram of structure geometry and mesh

composition

during

simulation.

(PDF)

Movie S1 (AVI), Movie S2 (AVI)

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected] and [email protected]

Author Contributions


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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

ACKNOWLEDGMENT

This research was supported by a grant of the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HR14C-0007-060018, and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1E1A1A01075147 & NRF2018M3A9D7079485).

REFERENCES (1) Srinivasan, S.; Chhatre, S. S.; Guardado, J. O.; Park, K.-C.; Parker, A. R.; Rubner, M. F.; McKinley, G. H.; Cohen, R. E. Quantification of Feather Structure, Wettability and Resistance to Liquid Penetration. J. R. Soc., Interface 2014, 11 (96), 20140287.


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Page 31 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(2) Bixler, G. D.; Bhushan, B. Rice-and Butterfly-wing Effect Inspired Self-cleaning and Low Drag Micro/Nanopatterned Surfaces in Water, Oil, and Air Flow. Nanoscale 2014, 6 (1), 76-96. (3) Guo, H.; Fuchs, P.; Casdorff, K.; Michen, B.; Chanana, M.; Hagendorfer, H.; Romanyuk, Y. E.; Burgert, I. Bio‐Inspired Superhydrophobic and Omniphobic Wood Surfaces. Adv. Mater. Interfaces 2017, 4 (1), 1600289. (4) Latthe, S. S.; Terashima, C.; Nakata, K.; Fujishima, A. Superhydrophobic Surfaces Developed by Mimicking Hierarchical Surface Morphology of Lotus Leaf. Molecules 2014, 19 (4), 4256-4283. (5) Nishimoto,

S.;

Bhushan,

B.

Bioinspired

Self-cleaning

Surfaces

with

Superhydrophobicity, Superoleophobicity, and Superhydrophilicity. RSC Adv. 2013, 3 (3), 671-690. (6) Tian, Y.; Su, B.; Jiang, L. Interfacial Material System Exhibiting Superwettability.

Adv. Mater. 2014, 26 (40), 6872-6897. (7) Verho, T.; Bower, C.; Andrew, P.; Franssila, S.; Ikkala, O.; Ras, R. H. Mechanically Durable Superhydrophobic Surfaces. Adv. Mater. 2011, 23 (5), 673-678.


31


Page 32 of 44

(8) Wang, S.; Liu, K.; Yao, X.; Jiang, L. Bioinspired Surfaces with Superwettability: New Insight on Theory, Design, and Applications. Chem. Rev. 2015, 115 (16), 8230-8293. (9) Srinivasan, S.; Choi, W.; Park, K. C.; Chhatre, S. S.; Cohen, R. E.; McKinley, G. H. Drag Reduction for Viscous Laminar Flow on Spray-coated Non-wetting Surfaces. Soft

Matter. 2013, 9(24), 5691-5702. (10) Jin, M.; Feng, X.; Xi, J.; Zhai, J.; Cho, K.; Feng, L.; Jiang, L. Super‐hydrophobic PDMS Surface with Ultra‐low Adhesive Force. Macromol. Rapid Commun. 2005, 26(22), 1805-1809. (11) Kang, S. M.; Lee, C.; Kim, H. N.; Lee, B. J.; Lee, J. E.; Kwak, M. K.; Suh, K. Y. Directional Oil Sliding Surfaces with Hierarchical Anisotropic Groove Microstructures.

Adv. Mater. 2013, 25 (40), 5756-5761. (12) Jokinen, V.; Kankuri, E.; Hoshian, S.; Franssila, S.; Ras, R. H. Blood‐Repellent Surfaces: Superhydrophobic Blood‐Repellent Surfaces, Adv. Mater. 2018, 30(24), 1870173.


32

Page 33 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(13) Golovin, K.; Lee, D. H.; Mabry, J. M.; & Tuteja, A. Transparent, Flexible, Superomniphobic Surfaces with Ultra‐Low Contact Angle Hysteresis. Angew.

Chem. 2013, 52(49), 13007-13011. (14) Wong, T.-S.; Kang, S. H.; Tang, S. K.; Smythe, E. J.; Hatton, B. D.; Grinthal, A.; Aizenberg, J. Bioinspired Self-repairing Slippery Surfaces with Pressure-stable Omniphobicity. Nature 2011, 477 (7365), 443. (15) Hong, D.; Bae, K.; Hong, S.-P.; Park, J. H.; Choi, I. S.; Cho, W. K. Mussel-inspired, Perfluorinated Polydopamine for Self-cleaning Coating on Various Substrates. Chem.

Commun. 2014, 50 (79), 11649-11652. (16) Leslie, D. C.; Waterhouse, A.; Berthet, J. B.; Valentin, T. M.; Watters, A. L.; Jain, A.; Kim, P.; Hatton, B. D.; Nedder, A.; Donovan, K. A Bioinspired Omniphobic Surface Coating on Medical Devices Prevents Thrombosis and Biofouling. Nat. Biotechnol. 2014, 32 (11), 1134-1140. (17) Mazumder, P.; Jiang, Y.; Baker, D.; Carrilero, A.; Tulli, D.; Infante, D.; Hunt, A. T.; Pruneri, V. Superomniphobic, Transparent, and Antireflection Surfaces based on Hierarchical Nanostructures. Nano Lett. 2014, 14 (8), 4677-4681.


33


Page 34 of 44

(18) Wang, J.; Kato, K.; Blois, A. P.; Wong, T.-S. Bioinspired Omniphobic Coatings with a Thermal Self-Repair Function on Industrial Materials. ACS Appl. Mater. Interfaces 2016, 8 (12), 8265-8271. (19) Liu, P.; Zhang, H.; He, W.; Li, H.; Jiang, J.; Liu, M.; Sun, H.; He, M.; Cui, J.; Jiang, L.; Yao, X. Development of “Liquid-like” Copolymer Nanocoatings for Reactive OilRepellent Surface. ACS Nano 2017, 11(2), 2248-2256. (20) Cao, M.; Guo, D.; Yu, C.; Li, K.; Liu, M.; Jiang, L. Water-repellent Properties of Superhydrophobic and Lubricant-infused “Slippery” Surfaces: A Brief Study on the Functions and Applications. ACS Appl. Mater. Interface 2015, 8(6), 3615-3623. (21) Nickerl, J.; Tsurkan, M.; Hensel, R.; Neinhuis, C.; Werner, C. The Multi-layered Protective Cuticle of Collembola: a Chemical Analysis. J. R. Soc., Interface 2014, 11 (99), 20140619. (22) Hensel, R.; Helbig, R.; Aland, S.; Voigt, A.; Neinhuis, C.; Werner, C. Tunable NanoReplication to Explore the Omniphobic Characteristics of Springtail Skin. NPG Asia Mater. 2013, 5 (2), e37.


34

Page 35 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Hensel, R.; Finn, A.; Helbig, R.; Braun, H. G.; Neinhuis, C.; Fischer, W. J.; Werner, C. Biologically Inspired Omniphobic Surfaces by Reverse Imprint Lithography. Adv.

Mater. 2014, 26 (13), 2029-2033. (24) Darmanin, T.; Guittard, F. Superhydrophobic and Superoleophobic Properties in Nature. Mater. Today 2015, 18 (5), 273-285. (25) Hensel, R.; Neinhuis, C.; Werner, C. The Springtail Cuticle as a Blueprint for Omniphobic Surfaces. Chem. Soc. Rev. 2016, 45 (2), 323-341. (26) Kang, H.; Lee, J. S.; Chang, W. S.; Kim, S. H. Liquid‐impermeable Inverse Opals with Invariant Photonic Bandgap. Adv. Mater. 2015, 27 (7), 1282-1287. (27) Golovin, K.; Lee, D. H.; Mabry, J. M.; Tuteja, A. Transparent, Flexible, Superomniphobic Surfaces with Ultra‐Low Contact Angle Hysteresis. Angew. Chem. Int.

Ed. 2013, 52 (49), 13007-13011. (28) Kim, J. H.; Shim, T. S.; Kim, S. H. Lithographic Design of Overhanging Microdisk Arrays Toward Omniphobic Surfaces. Adv. Mater. 2016, 28 (2), 291-298.


35


Page 36 of 44

(29) Choi, H.-J.; Choo, S.; Shin, J.-H.; Kim, K.-I.; Lee, H. Fabrication of Superhydrophobic and Oleophobic Surfaces with Overhang Structure by Reverse Nanoimprint Lithography. J. Phys. Chem. C 2013, 117 (46), 24354-24359. (30) Tuteja, A.; Choi, W.; Mabry, J. M.; McKinley, G. H.; Cohen, R. E. Robust omniphobic surfaces. Proc Natl Acad Sci. 2008. 105(47), 18200-18205. (31) Nosonovsky, Michael. Multiscale Roughness and Stability of Superhydrophobic Biomimetic Interfaces. Langmuir 2007, 23(6), 3157-3161. (32) Tuteja, A.; Choi, W.; Ma, M.; Mabry, J. M.; Mazzella, S. A.; Rutledge, G. C.; McKinley, G. H.; Cohen, R. E. Designing Superoleophobic Surfaces. Science 2007, 318(5856), 1618-1622. (33) Liimatainen, V.; Sariola, V.; Zhou, Q. Controlling Liquid Spreading using Microfabricated Undercut Edges. Adv. Mater. 2013, 25 (16), 2275-2278. (34) Hensel, R.; Helbig, R.; Aland, S.; Braun, H.-G.; Voigt, A.; Neinhuis, C.; Werner, C. Wetting Resistance at its Topographical Limit: the Benefit of Mushroom and Serif T Structures. Langmuir 2013, 29 (4), 1100-1112.


36

Page 37 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Kota, A. K.; Kwon, G.; Tuteja, A. The Design and Applications of Superomniphobic Surfaces. NPG Asia Mater. 2014, 6 (7), e109. (36) Wu, H.; Yang, Z.; Cao, B.; Zhang, Z.; Zhu, K.; Wu, B.; Jiang, S.; Chai, G. Wetting and Dewetting Transitions on Submerged Superhydrophobic Surfaces with Hierarchical Structures. Langmuir 2017, 33 (1), 407-416. (37) Bellanger, H.; Darmanin, T.; Taffin de Givenchy, E.; Guittard, F. Chemical and Physical Pathways for the Preparation of Superoleophobic Surfaces and Related Wetting Theories. Chem. Rev. 2014, 114 (5), 2694-2716. (38) Cassie, A.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546-551. (39) Giacomello, A.; Meloni, S.; Chinappi, M.; Casciola, C. M. Cassie–Baxter and Wenzel states on a Nanostructured Surface: Phase Diagram, Metastabilities, and Transition Mechanism by Atomistic Free Energy Calculations. Langmuir 2012, 28 (29), 10764-10772. (40) Liu, T.; Kim, C.-J. Turning a Surface Superrepellent even to Completely Wetting Liquids. Science 2014, 346, 1096-1100.


37


Page 38 of 44

(41) Murakami, D.; Jinnai, H.; Takahara, A. Wetting Transition from the Cassie–Baxter State to the Wenzel State on Textured Polymer Surfaces. Langmuir 2014, 30 (8), 20612067. (42) Wenzel, R. N. Resistance of Solid Surfaces to Wetting by Water. Ind. Eng. Chem. 1936, 28 (8), 988-994. (43) Kota, A. K.; Li, Y.; Mabry, J. M.; Tuteja, A. Hierarchically structured superoleophobic surfaces with ultralow contact angle hysteresis. Adv. Mater. 2012, 24(43), 5838-5843. (44) Zhu, P.; Kong, T.; Tang, X.; Wang, L. Well-defined Porous Membranes for Robust Omniphobic Surfaces via Microfluidic Emulsion Templating. Nat. Commun. 2017, 8, 15823. (45) Chen, X.; Weibel, J. A.; Garimella, S. V. Water and Ethanol Droplet Wetting Transition during Evaporation on Omniphobic Surfaces. Sci. Rep. 2015, 5, 17110. (46) Young, T. An Essay on the Cohesion of Fluids. Philos. Trans. R. Soc. London. 1805, 95, 65-87.


38

Page 39 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(47) Kong, J.-H.; Kim, T.-H.; Kim, J. H.; Park, J.-K.; Lee, D.-W.; Kim, S.-H.; Kim, J.-M. Highly Flexible, Transparent and Self-cleanable Superhydrophobic Films Prepared by a Facile and Scalable Nanopyramid Formation Technique. Nanoscale 2014, 6 (3), 14531461. (48) Toma, M.; Loget, G.; Corn, R. M. Flexible Teflon Nanocone Array Surfaces with Tunable Superhydrophobicity for Self-cleaning and Aqueous Droplet Patterning. ACS

Appl. Mater. Interfaces 2014, 6 (14), 11110-11117. (49) Tsui, K. H.; Lin, Q.; Chou, H.; Zhang, Q.; Fu, H.; Qi, P.; Fan, Z. Low‐Cost, Flexible, and Self‐Cleaning 3D Nanocone Anti‐Reflection Films for High‐Efficiency Photovoltaics.

Adv. Mater. 2014, 26 (18), 2805-2811. (50) Kim, T.-H.; Ha, S.-H.; Jang, N.-S.; Kim, J.; Kim, J. H.; Park, J.-K.; Lee, D.-W.; Lee, J.; Kim, S.-H.; Kim, J.-M. Simple and Cost-effective Fabrication of Highly Flexible, Transparent Superhydrophobic Films with Hierarchical Surface Design. ACS Appl. Mater.

Interfaces 2015, 7 (9), 5289-5295.


39


Page 40 of 44

(51) Mates, J. E.; Bayer, I. S.; Palumbo, J. M.; Carroll, P. J.; Megaridis, C. M. Extremely Stretchable and Conductive Water-repellent Coatings for Low-cost Ultra-flexible Electronics. Nat. Commun. 2015, 6, 8874. (52) Wong, W. S.; Nasiri, N.; Liu, G.; Rumsey‐Hill, N.; Craig, V. S.; Nisbet, D. R.; Tricoli, A. Flexible Transparent Hierarchical Nanomesh for Rose Petal‐like Droplet Manipulation and Lossless Transfer. Adv. Mater. Interfaces 2015, 2 (9), 1500071. (53) Wang, L.; Gong, Q.; Zhan, S.; Jiang, L.; Zheng, Y. Robust Anti‐Icing Performance of a Flexible Superhydrophobic Surface. Adv. Mater. 2016, 28 (35), 7729-7735. (54) Wang, N.; Lu, Y.; Xiong, D.; Carmalt, C. J.; Parkin, I. P. Designing Durable and Flexible Superhydrophobic Coatings and its Application in Oil Purification. J. Mater.

Chem. A 2016, 4 (11), 4107-4116. (55) Ju, J.; Yao, X.; Hou, X.; Liu, Q.; Zhang, Y. S.; Khademhosseini, A. A Highly Stretchable and Robust Non-fluorinated Superhydrophobic Surface. J. Mater. Chem. A 2017, 5 (31), 16273-16280. (56) Rather, A. M.; Manna, U. Stretchable and Durable Superhydrophobicity that acts Both in Air and Under Oil. J. Mater. Chem. A 2017, 5 (29), 15208-15216.


40

Page 41 of 44 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(57) Li, N.; Wu, L.; Yu, C.; Dai, H.; Wang, T.; Dong, Z.; Jiang, L. Ballistic Jumping Drops on Superhydrophobic Surfaces via Electrostatic Manipulation. Adv. Mater. 2018, 30(8), 1703838. (58) Gaddam, A.; Agrawal, A.; Joshi, S. S.; Thompson, M. C. Utilization of Cavity Vortex to Delay the Wetting Transition in One-dimensional Structured Microchannels. Langmuir 2015, 31(49), 13373-13384. (59) Huang, X. J.; Lee, J. H.; Lee, J. W.; Yoon, J. B.; Choi, Y. K. A One‐Step Route to a

Perfectly

Ordered

Wafer‐Scale

Microbowl

Array

for

Size‐Dependent

Superhydrophobicity. Small 2008, 4(2), 211-216. (60) Wu, H.; Yang, Z.; Cao, B.; Zhang, Z.; Zhu, K.; Wu, B.;Jiang, S.; Chai, G. Wetting and Dewetting Transitions on Submerged Superhydrophobic Surfaces with Hierarchical Structures. Langmuir 2016, 33(1), 407-416. (61) Domingues, E. M.; Arunachalam, S.; Mishra, H. Doubly Reentrant Cavities Prevent Catastrophic Wetting Transitions on Intrinsically Wetting Surfaces. ACS Appl. Mater.

Interfaces 2017, 9(25), 21532-21538.


41


Page 42 of 44

(62) Grewal, H. S.; Cho, I.-J.; Oh, J.-E.; Yoon, E.-S. Effect of Topography on the Wetting of Nanoscale Patterns: Experimental and Modeling Studies. Nanoscale 2014, 6 (24), 15321-15332. (63) Zhang, R. L.; Di, Q. F.; Wang, X. L.; Gu, C. Y. Numerical Study of Wall Wettabilities and Topography on Drag Reduction Effect in Micro-channel Flow by Lattice Boltzmann Method. J. Hydrodyn. 2010, 22(3), 366-372. (64) Zaretskiy, Y.; Geiger, S.; Sorbie, K. Direct Numerical Simulation of Pore-scale Reactive Transport: Applications to Wettability Alteration during Two-phase Flow. Int. J.

Oil, Gas Coal Technol. 2012, 5(2-3), 142-156. (65) Huang, J. J.; Huang, H.; Wang, X. Numerical Study of Drop Motion on a Surface with Stepwise Wettability Gradient and Contact Angle Hysteresis. Phys. Fluids 2014, 26(6), 062101. (66) Wang,

Y.;

Chen,

S.

Numerical

Study

on

Droplet

Sliding

across

Micropillars. Langmuir 2015, 31(16), 4673-4677. (67) Huhtamäki, T.; Tian, X.; Korhonen, J. T.; Ras, R. H. Surface-wetting Characterization using Contact-angle Measurements. Nat. Protoc. 2018, 13(7), 1521.


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(68) Verho, T.; Bower, C.; Andrew, P.; Franssila, S.; Ikkala, O.; Ras, R. H. Mechanically Durable Superhydrophobic Surfaces. Adv. Mater. 2011, 23(5), 673-678.


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Table of Contents


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Flexible and Stable Omniphobic Surfaces Based on Biomimetic

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