Article pubs.acs.org/JPCC
Icephobicity of Penguins Spheniscus Humboldti and an Artificial Replica of Penguin Feather with Air-Infused Hierarchical Rough Structures Shuying Wang,‡ Zhongjia Yang,† Guangming Gong,† Jingming Wang,*,† Juntao Wu,† Shunkun Yang,*,§ and Lei Jiang†,∥ †
Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, P. R. China ‡ Aerospace Research Institute of Materials and Processing Technology, Beijing 100076, P. R. China § School of Reliability and Systems Engineering, Beihang University, Beijing 100191, P. R. China ∥ Laboratory of Bioinspired Smart Interfacial Science, Technical Institute of Physics and Chemistry, CAS, Beijing 100190, P. R. China S Supporting Information *
ABSTRACT: Although penguins live in the world’s coldest environment, frost and ice are seldom found on their feathers. That is to say, their feathers exhibit excellent antifrosting or anti-icing properties. We found that their air-infused microscale and nanoscale hierarchical rough structures endow the body feathers of penguins Spheniscus humboldti with hydrophobicity (water CA ≈ 147°) and antiadhesion characteristics (water adhesive force ≈ 23.4 μN), even for supercooled water microdroplets. A polyimide nanofiber membrane with novel microstructures was prepared on an asymmetric electrode by electrospinning, acting as an artificial replica of a penguin’s body feather. The unique microstructure of the polyimide nanofiber membrane results in a density gradient of the surface chemical substance, which is crucial to the formation of gradient changes of the contact angle and adhesive force. With decrease of the density of the surface chemical substance (i.e., with increase of the distance between adjacent fibers), the static water contact angles decreased from ∼154° to ∼105° and the water adhesion forces increased from 37 to 102 μN. Polyimide nanofibers pin a few supercooled water microdroplets. By increasing the distance of adjacent polyimide fibers, coalescence between the pinned water microdroplets was prevented. The polyimide fiber membrane achieved icephobicity.
1. INTRODUCTION
However, many researchers found that the use of superhydrophobic surfaces was not always successful in anti-icing applications, especially at high humidities and ultralow temperatures. At high humidities, moisture condenses in the rough structure of the superhydrophobic surfaces, and droplets grow and coalescence rapidly to form an ice layer on the surface.19,20 At ultralow temperatures, frost and ice nucleation occurs on all areas of the superhydrophobic surface textures, leading to the loss of superhydrophobic properties and an increase in ice adhesion strength.21,22 In fact, superhydrophobicity cannot reduce ice adhesion, and the ice adhesion strength on flat hydrophilic and hydrophobic surfaces was sometimes lower than on structured superhydrophilic and superhydrophobic surfaces.23,24 It was found that the force needed to detach ice pieces from a surface depends on the receding contact angle and the initial size of interfacial cracks.25 Even
Many biological surfaces exhibit interesting wetting or dewetting properties to enable survival in complex living environments.1−5 The superhydrophobic and self-cleaning effect of the lotus leaf is a typical example. On superhydrophobic and self-cleaning surfaces, deposited water droplets remain in a nonwetting Cassie−Baxter state,6 resulting from air trapping inside the textured surface.7,8 The trapped air minimizes interaction between the water droplet and solid surfaces, and the water droplet slides easily on superhydrophobic surfaces when they are slightly tilted.9,10 Thus, the energy barrier to the removal of water droplets from superhydrophobic surfaces is decreased. Many researchers hypothesize that superhydrophobic surfaces would be successful in producing an anti-icing effect by repelling water droplets and removing them from a surface before they can freeze.11−16 Furthermore, the trapped air pockets effectively form a thermal barrier to hinder heat transfer during icing and have the capacity to reduce ice adhesion strength, so that ice easily slips off superhydrophobic surfaces.17,18 © XXXX American Chemical Society
Special Issue: Kohei Uosaki Festschrift Received: December 16, 2015 Revised: February 2, 2016
A
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 1. Hierarchical micro- and nanostructures (b,c) and water contact angle (d) on body feathers of penguins Spheniscus humboldti. (a) Photograph of the body feather; environmental scanning electron micrographs of (b1) the rachis and barb; (b2) the barbules with the hamuli; (b3) elaborate wrinkles on the barbules and hamuli; (c1) the tips of barbules without hamuli; and (c2) oriented nanoscaled grooves on the barbules (∼100 nm deep).
2. EXPERIMENTAL METHODS 2.1. Preparation of Spheniscus humboldti Body Feathers. Specimens of the Spheniscus humboldti body feathers were obtained from Beijing Pacific Underwater World. The feathers were cut into square pieces, about 4 × 4 mm2. The specimens were immersed in a 95.0 vol % ethanol solution for 10 min at room temperature and then dried in an oven at 70 °C for 1 h. 2.2. Preparation of Polyimide Fiber Membrane. Polyamic acid solution, a precursor of polyimide, was synthesized using 1,2,4,5-benzenetetracarboxylic anhydride and 4,4′-diaminodiphenyl ether in dimethylformamide (Beijing Chemicals, Beijing, dehydrated before use). An ordered polyamic acid fiber membrane with novel microstructures was fabricated using high-pressure electrostatic spinning. The experimental setup is shown in Figure S1. The electric field is provided using a blunt metal needle filled with the polymer solution. A special electrode is designed to collect the ejected fibers. The special electrode consists of two ends, a triangular electrode end and a curved electrode end. The voltage is 18 kV. The temperature is maintained at 40 °C. The humidity is less than 10%. The distance between spinneret and electrode is 25 cm. The ejected fibers are stretched in the air before reaching the special electrode. The nanofibers were arranged radially in a pattern from dense to sparse along the direction from the triangular electrode end to the curved electrode end. A series of sequential thermal treatments, including 0.5 h at 80 °C, 1 h at 120 °C, 1 h at 180 °C, 0.5 h at 250 °C, and 1 h at 300 °C, was applied, to convert the polyamic acid fibers to polyimide fibers. 2.3. Characterization. The structures of the Spheniscus humboldti feathers and the oriented polyimide fiber membrane were characterized using an environmental scanning electron microscope (Quanta ×50 FEG, America) at 4.2 and 10.0 kV under high-vacuum mode, respectively. All samples for
surfaces with a very high receding contact angle may have strong adhesion to ice if the cracks are small. Furthermore, during icing and deicing cycles, ice accretion on a superhydrophobic surface eventually causes gradual damage of the surface microstructure.26,27 Penguins, which live in the world’s coldest environments, have a thick layer of feathers that prevent the penetration of cold seawater to the skin and play a role in insulation. Much effort has been devoted to investigating how the morphology of the contour, downy afterfeathers function as thermal insulators28 and their material composition, as well as how this affects the mechanical performance of penguins.29,30 As they are the fastest swimming birds, frost and ice can be seldom found on penguins’ feathers. That is to say, their feathers exhibit excellent antifrosting and anti-icing properties. However, there is little research focusing on the wettability and antifrosting or anti-icing properties of penguin’s feathers. We investigated the antifrosting and anti-icing properties of penguin’s body feathers. We found that penguin’s body feathers exhibit excellent hydrophobicity and the antiadhesion characteristics needed to repel supercool water microdroplets. Their microscale and nanoscale hierarchical rough structures trapped air, to prevent water adhesion and coalescence. Inspired by this, a polyimide nanofiber membrane with novel microstructures was prepared on an asymmetric electrode by electrospinning. The unique microstructure of the polyimide nanofiber membrane results in a gradient density of the surface chemical substance, which is crucial to the formation of gradient changes in the water contact angle and adhesive force. With increasing distance between adjacent polyimide fibers, coalescence of pinned water microdroplets was prevented by the trapped air, and the polyimide fiber membrane achieved icephobicity. B
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 2. Series of video stills illustrating adhesion process of supercooled water microdroplets on the tips of barbules without hamuli (a−f) and on barbs with hamuli (a′−f′) at temperatures of −5 °C.
3. RESULTS AND DISCUSSION 3.1. Characterization of the Penguin Feathers and Their Superhydrophobicity. Environmental scanning electron micrographs of the body feathers of penguins Spheniscus humboldti are illustrated in Figure 1. Body feathers are the feathers that cover most of the penguin body’s (back and front) surface. The body feathers are composed of a rachis and two pinnae separated by the rachis (Figure 1a). The barb in the pinna is fibriform; barbs are arranged in parallel along the rachis at an angle of 20°. The length and the diameter of the barbs are 5−7 mm and 25−30 μm, respectively (Figure 1b1). On the barb there are barbules, the arrangement of which is similar to the ramus. The angle between the ramus and the barbules is about 40°. The average length and diameter of the barbules are ∼300 μm and ∼7 μm, respectively. Numerous hamuli can be found on the barbules, perpendicularly hooked on the barbules at a spacing of ∼20 μm, with a diameter of ∼3 μm (inset in Figure 1b2). These hamuli hook together, constructing a rigorous three-dimensional microstructural network. Figure 1b3 demonstrates that there are many elaborate wrinkles on the barbules and hamuli. On the tips of the barbs, there are few hamuli (Figure 1c1). The distance between adjacent barbs was from a few micrometers to tens of micrometers. Nanoscale
environmental scanning electron microscopy were sputtered with a thin layer of gold (2 nm) before observation. Contact angles were measured using an optical contact angle meter system (OCA20, Dataphysics Instruments GmbH, Germany) by depositing a deionized water droplet (3 μL) using the sessile drop method. A high-speed camera acquisition system was applied to take real-time photographs and videos for further analysis of the adhesion processes of the water microdroplets. Supercooled deionized water microdroplets were sprayed on the samples at an environmental temperature of −5 °C. Adhesive forces were measured by fixing a water droplet (3 μL) on a copper spiral in a microelectronic balance system (DCAT11, Dataphysics, Germany). The velocity of the platform is 0.05 mm/s. During the whole adhesion force testing process, a camera was applied to take real-time videos to illustrate the morphology changing processes of the droplets. In order to investigate the behavior of the sprayed supercooled deionized water microdroplets on penguin feathers under the state similar to their natural survival conditions, only rachis were fixed on a substrate, and the barbules were not fixed. The samples were put in a transparent chamber (35 cm × 35 cm × 35 cm). The temperature in the chamber can be kept constant from room temperature to −15 °C. C
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C grooves, ∼100 nm deep, are oriented along the barbs (Figure 1c2). The microscopic and nanoscopic hierarchical rough structures of the back feather surface effectively prevent the infiltration of water. Air pockets trapped in the rough microstructures reduce the surface contact area between the body feather and water droplets. The equilibrium static contact angle of 3 μL volume droplets is 147 ± 1.5°, exhibiting hydrophobicity (Figure 1d). In addition, the adhesive force between a single barb surface (with hamuli) and water droplets reached a maximum of 23.4 μN (see Figure S2). The water repellency of the feathers is greatly increased by its structural features, including the diameter and spacing of the barbs and barbules. However, the contribution of the feather structure to the hydrophobicity is determined not by the absolute value of the radii of the barbs and their distance apart, but by the ratio of the center distance of two barbs and the increasing radius of a single barb radius.31,32 3.2. Anti-Icing and Deicing Properties of the Hydrophobic Body Feather of Penguins Spheniscus humboldti. The penguin Spheniscus humboldti is a South American penguin that breeds in coastal Chile and Peru. The penguin lives in the environment with the temperature no less than −10 °C. However, it always swims in the cold water current (always with the temperature less than 0 °C) from the Atlantic. Thus, the adhesion process of supercooled deionized water microdroplets (with the temperature of ∼−5 °C) on different parts of the body feather was investigated at −5 °C for demonstrating the anti-icing and deicing properties of the hydrophobic body feathers of penguins Spheniscus humboldti. Besides, in order to simulate the state at their natural survival conditions, only rachis were fixed, and the barbules were not fixed. A series of video stills showing the adhesion of representative supercooled water microdroplets on the tips of the barbules without hamuli and on barbs with hamuli is given in Figure 2. After the supercooled water microdroplets were sprayed, they could not adhere to the tips of the barbules in the first few seconds (Figure 2a). Then a few supercooled water microdroplets were captured on the barbules. As time passed, more supercooled water microdroplets adhered (Figure 2b,c). However, the stuck microdroplets easily detached from the barbules (Figure 2d,e). Finally, in the whole spray process, a few water microdroplets adhered to the tips of the barbules (Figure 2b,c). It is probable that the air current produced by the spray blew the water microdroplets away from the barbule surfaces. After several hours, supercooled water microdroplets repeated the adhering and detaching cycles. Frost and ice could not be found on the barbules at −5 °C. Because of the low adhesion force between the barbule surfaces and the water microdroplets, the feathers exhibited excellent icephobicity. On the barb surfaces with hamuli, the supercool water microdroplets began to adhere to the barbs with hamuli at t = 12.48 s (Figure 2a′,b′), after which more water microdroplets can be captured on the rami surfaces (Figure 2c′,d′). During the adhesion process, the coalescence of water microdroplets was achieved under gravity and during spraying (Figure 2e′,f′). The size of the barbules without hamuli is larger than that of the barbs with hamuli. Moreover, under the air current of spay, the movement of the barbs with hamuli is much easier than that of the barbules without hamuli. Therefore, the pictures of (a′−f′) are mistier than the pictures of (a−f). The stuck microdroplets stayed on the barb surfaces for a longer period before detaching (>2 min). Although the existence of hamuli can enhance the roughness and then increase the hydrophobicity of the body
feathers, the increased specific surface area provides more opportunities for microdroplet adhesion. However, the trapped air effectively forms a thermal barrier to hinder heat transfer during icing and has the capacity to reduce ice adhesion strength. Thus, after 3−4 h, frost could be found on the barbule surface at −5 °C. Therefore, hydrophobicity is a necessary but not sufficient condition for anti-icing applications.23,33 3.3. Mathematical Analysis. A model is proposed to elucidate the hydrophobicity and icephobicity caused by the hierarchical microstructures and nanostructures of the body feathers (Figure 3). We selected the hamulus as the main object
Figure 3. Model to elucidate hydrophobicity and icephobicity caused by the hierarchical microstructures and nanostructures of the body feathers. (a) Schematic diagram of oriented barb, barbules, and hamuli, forming a three-dimensional microstructural network on the surface of the back feathers. (b) Contact between water microdroplets and hamuli. (c) Contact between water microdroplets and nanogrooves.
of study because it is a fine structure with smaller scales that hook together to construct a rigorous three-dimensional microstructural network in the body feather. The threedimensional microstructural network is illustrated in Figure 3a. During the whole spraying process, the supercooled water microdroplets cannot enter the hamuli but remain on surface (Figure 3b). The intrinsic water contact angle θ0 of arachidic acid,34 which covers the hamulus, is about 106°, indicating that the chemical component is not enough to attract the prominent hydrophobicity of the hamulus. On the basis of the Cassie− Baxter law for surface wettability,6 the contact state between the water microdroplets and the hamuli can be calculated as follows: cos θr = (π − θ)f cos θ − (1 − f sin θ )
(1)
where θr is the apparent water contact angle on the body feather and f is the air−water interface per unit apparent surface area
f = d′ / L ′ where d′ and L′ are the mean diameter and spacing of the hamuli, respectively. According to measurements of the microstructures, f is ∼0.39. To achieve superhydrophobicity for θr ≈ 147°, the body feather must have an intrinsic contact angle θ of not less than 116°. However, this is impossible for a smooth hamulus because θ = 106°. Thus, the oriented hamuli themselves are not sufficient to induce the excellent hydrophobicity of the feathers. D
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 4. (a) Photograph, (b1−b3) environmental scanning electron micrographs, and (c) water contact angle and adhesion force of the gradient polyimide nanofiber membrane at different positions. CA, contact angle.
arranged radially in a pattern from dense to sparse along the direction from the triangular electrode to the curved electrode (Figure 4b). The diameters of the polyimide nanofibers were uniform (100−500 nm), and their surfaces were smooth. The distance between the adjacent fibers was from a few micrometers to tens of micrometers. The radial patterned nanofibers are similar to the structures of the barb tips (Figure 1c1). Furthermore, the rest of the nanofibers randomly overlapped on the radial patterned ones, resulting in the construction of a rigorous three-dimensional microstructural network. The unique microstructure of polyimide nanofiber membrane results in a density gradient of the surface chemical substance, which is crucial to producing the required variations in contact angle and adhesive force (Figure 4c). The shape of the water droplet was nearly spherical, and the fabricated membrane exhibited a prominent superhydrophobicity with a high static water contact angle of ≈154° and a low adhesion force (∼37 μN) at the position closest to the triangular electrode (Figure S3 and S4). At the position closet to the triangular electrode, the arrangement of the nanofibers is dense. The gaps between the fibers were quite small. Lots of fibers even overlapped with each other. The water droplets cannot easily infiltrate into the small gap between the overlapping fibers, and their wetting state is the Cassie state. Gradually away from the triangular electrode, the distance between adjacent fibers increases. Water droplets immersed into the larger gaps in the fiber membrane more easily. The static water contact angles decreased, and the adhesion forces increased. The wetting state of water droplets transited to the Wenzel and
The grooved nanostructures on the hamulus surface are necessary to yield a larger θ than θ0. According to the highresolution images of the oriented nanoscale grooves, the average width and depth of the nanogrooves are ∼500 and ∼100 nm, respectively. The cross-section of nanogrooves on hamuli is illustrated in Figure 3c. The contact state between the water microdroplets and the nanogrooves can be calculated as cos θ = (π − θ0)f ′ cos θ0 − (1 − f ′ sin θ0)
(2)
where f ′ is the fraction of wetted projection area f ′ = 2d /L
where d/2 and L are the radius of curvature and the spacing of the nanogrooves, respectively. The measured values, f ′ ≈ 0.92 and θ0 = 106°, give θ ≈ 116°, which is consistent with the predicted results. Consequently, the excellent hydrophobicity of the body feathers is a combination of low-surface-energy chemical components and multiscaled structures. 3.4. Polyimide Fiber Membranes (Artificial Replica of Penguin Feathers) and Their Wettability and Anti-Icing Properties. Inspired by the three-dimensional microstructural network of the penguin body feather, a radial polyimide nanofiber membrane with novel microstructures was prepared on an asymmetric electrode by electrospinning (Figure 4a). Polyimide has good mechanical strength at low temperature.35,36 The polyimide fiber cannot be brittle fractured in liquid nitrogen, which is similar to penguin feather. Polyimide nanofiber membrane consists of numerous oriented polyimide fibers. A large proportion of polyimide nanofibers were E
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
Figure 5. Series of video stills illustrating adhesion process of supercool water microdroplets on gradient polyimide fiber membrane.
Cassie coexistence state.37 At the position where the distance between the adjacent fibers reached a maximum (close to the curved electrode), water droplets immersed into the larger gaps completely. The static water contact angles decreased to 105.1°, and the adhesion forces increased to 102 μN. With increasing the distance between adjacent fibers, water droplets entered the microscopic gaps between fibers, and the wetting state changed from the Cassie state to the Wenzel state.37 The process of adhesion of supercooled deionized water microdroplets onto the polyimide nanofiber membrane with novel microstructures was investigated. A series of video stills illustrating the supercool water microdroplet adhesion process at −5 °C is given in Figure 5. After the supercooled water microdroplets were sprayed, they could not adhere to the microstructures in the first few seconds (Figure 5a). The supercooled water microdroplets began to adhere to the fibers at t = 6.04 s (microdroplet 1, Figure 5b). As time passed, more supercooled water microdroplets adhered to the polyimide fiber membrane (microdroplets 2 to 7, Figure 5c). After a few seconds, most of the adhered microdroplets could detach from the polyimide fiber membrane (microdroplets 2 to 4, 6, and 7). However, there are more supercooled water microdroplets adhered at other positions (Figure 5d). If the adhesive microdroplets coalesced with other microdroplets with similar diameter, self-propelled jumping of the combination would happen. The combination detached from the nanofiber. The diameter of coalescing condensed microdroplets in jumping events and the frequency of jumping events can be tuned by the size of microstructures.38,39 If the distance between the adjacent fibers was large enough, (i.e., larger than the water microdroplets), coalescence of water microdroplets did not occur under gravity or during spraying. After 3−4 h, frost and ice could be found on the sparse part of the polyimide fiber membrane surface at −5 °C. Therefore, the polyimide fiber membrane could achieve icephobicity by choosing an effective distance between the adjacent nanofibers (i.e., the adhesive water microdroplets).
4. CONCLUSIONS The microscopic and nanoscopic hierarchical rough structures endow the penguin’s body feathers with excellent hydrophobicity and antiadhesion characteristics against supercooled water microdroplets. A polyimide nanofiber membrane with novel microstructures was prepared on an asymmetric electrode by electrospinning. The unique microstructure of the polyimide nanofiber membrane formed a gradient density of the surface chemical substance, which is crucial in forming the required gradient changes in contact angle and adhesive force. By increasing the distance between adjacent polyimide fibers, coalescence of pinned water microdroplets was prevented, and the polyimide fiber membrane achieved icephobicity.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.5b12298. Schematic diagram of the electrospinning process; force−distance curves between a single barb surface with hamuli and water droplets; PI fibers membrane with striking water repellence at the position closest to the triangular electrode; force−distance curves recorded between the water droplet contacts and the PI fibers membrane at the position closest to the triangular electrode (PDF)
■ ■
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS The authors thank the financial support by National Research Fund for Fundamental Key Projects (2013CB933000), National Natural Science Foundation (21121001 and 91127025), the Key Research Program of the Chinese Academy of Sciences (KJZD-EW-M01), the 111 Project (No. B14009), and Beijing Higher Education Young Elite Teacher Project (YETP1151). F
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
Article
The Journal of Physical Chemistry C
■
(26) Farhadi, S.; Farzaneh, M.; Kulinich, S. A. Anti-Icing Performance of Superhydrophobic Surfaces. Appl. Surf. Sci. 2011, 257, 6264−6269. (27) Kulinich, S. A.; Farhadi, S.; Nose, K.; Du, X. Superhydrophobic Surfaces: Are They Really Ice-Repellent? Langmuir 2011, 27, 25−29. (28) Dawson, C.; Vincent, J. F. V.; Jeronimidis, G.; Rice, G.; Forshaw, P. Heat Transfer through Penguin Feathers. J. Theor. Biol. 1999, 199, 291−295. (29) Taylor, J. R. E. Thermal Insulation of the Down and Feathers of Pygoscelid Penguin Chicks and the Unique Properties of Penguin Feathers. Auk 1986, 103, 160−168. (30) Bonser, R. H. C.; Dawson, C. The Mechanical Properties of Down Feathers from Gentoo Penguins (Pygoscelis Papua). J. Zool. 2000, 251, 545−547. (31) Rijke, A. M. The Water Repellency and Feather Structure of Cormorants, Phalacrocoracidae. J. Exp Biol. 1968, 48, 185−189. (32) Rijke, A. M. Wettability and Phylogenetic Development of Feather Structure in Water Birds. J. Exp. Biol. 1970, 52, 469−479. (33) Wang, F.; Shen, T.; Li, C.; Li, W.; Yan, G. Low Temperature Self-Cleaning Properties of Superhydrophobic Surfaces. Appl. Surf. Sci. 2014, 317, 1107−1112. (34) Bormashenko, E.; Bormashenko, Y.; Stein, T.; Whyman, G.; Bormashenko, E. Why do Pigeon Feathers Repel Water? Hydrophobicity of Pennae, Cassie−Baxter Wetting Hypothesis and Cassie− Wenzel Capillarity-Induced Wetting Transition. J. Colloid Interface Sci. 2007, 311, 212−216. (35) Bai, F.; Wu, J.; Gong, G.; Guo, L. A Flexible, Sandwiched HighPerformance Super-Insulation Fabric. J. Mater. Chem. A 2015, 3, 13198−13202. (36) Zhang, Y.; Wu, J.; Fu, S.; Yang, S.; Li, Y.; Fan, L.; Li, R. K. Y.; Li, L.; Yan, Q. Studies on Characterization and Cryogenic Mechanical Properties of Polyimide-Layered Silicate Nanocomposite Films. Polymer 2004, 45, 7579−7587. (37) Jiang, L.; Feng, L. Bioinspired Intelligent Nanostructured Interfacial Materials; Chemical Industry Press: Beijing, China, 2007. (38) He, M.; Wang, J.; Li, H.; Song, Y. Super-Hydrophobic Surfaces to Condensed Micro-Droplets at Temperatures below the Freezing Point Retard Ice/Frost Formation. Soft Matter 2011, 7, 3993−4000. (39) Zhang, Q.; He, M.; Chen, J.; Wang, J.; Song, Y.; Jiang, L. AntiIcing Surfaces Based on Enhanced Self-Propelled Jumping of Condensed Water Microdroplets. Chem. Commun. 2013, 49, 4516− 4518.
REFERENCES
(1) Barthlott, W.; Neinhuis, C. Purity of the Sacred Lotus, or Escape from Contamination in Biological Surfaces. Planta 1997, 202, 1−8. (2) Feng, L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D. Super-Hydrophobic Surfaces: From Natural to Artificial. Adv. Mater. 2002, 14, 1857−1860. (3) Zheng, Y.; Bai, H.; Huang, Z.; Tian, X.; Nie, F.; Zhao, Y.; Zhai, J.; Jiang, L. Directional Water Collection on Wetted Spider Silk. Nature 2010, 463, 640−643. (4) Gao, X.; Jiang, L. Biophysics: Water-Repellent Legs of Water Striders. Nature 2004, 432, 36−36. (5) Ju, J.; Bai, H.; Zheng, Y.; Zhao, T.; Fang, R.; Jiang, L. A MultiStructural and Multi-Functional Integrated Fog Collection System in Cactus. Nat. Commun. 2012, 3, 1247. (6) Cassie, A. B. D.; Baxter, S. Wettability of Porous Surfaces. Trans. Faraday Soc. 1944, 40, 546−551. (7) Sun, T.; Feng, L.; Gao, X.; Jiang, L. Bioinspired Surfaces with Special Wettability. Acc. Chem. Res. 2005, 38, 644−652. (8) Yao, X.; Song, Y.; Jiang, L. Applications of Bio-Inspired Special Wettable Surfaces. Adv. Mater. 2011, 23, 719−734. (9) Li, X.; Reinhoudt, D.; Crego-Calama, M. What Do We Need for A Superhydrophobic Surface? A Review on the Recent Progress in the Preparation of Superhydrophobic Surfaces. Chem. Soc. Rev. 2007, 36, 1350−1368. (10) Deng, X.; Mammen, L.; Butt, H. J.; Vollmer, D. Candle Soot as a Template for a Transparent Robust Superamphiphobic Coating. Science 2012, 335, 67−70. (11) Tourkine, P.; Le Merrer, M.; Quéré, D. Delayed Freezing on Water Repellent Materials. Langmuir 2009, 25, 7214−7216. (12) Kulinich, S. A.; Farzaneh, M. How Wetting Hysteresis Influences Ice Adhesion Strength on Superhydrophobic Surfaces. Langmuir 2009, 25, 8854−8856. (13) He, M.; Wang, J.; Li, H.; Song, Y. Superhydrophobic Surfaces to Condensed Micro-Droplets at Temperatures below the Freezing Point Retard Ice/Frost Formation. Soft Matter 2011, 7, 3993−4000. (14) Guo, P.; Zheng, Y.; Wen, M.; Song, C.; Lin, Y.; Jiang, L. Icephobic/Anti-Icing Properties of Micro/Nanostructured Surfaces. Adv. Mater. 2012, 24, 2642−2648. (15) Wen, M.; Wang, L.; Zhang, M.; Jiang, L.; Zheng, Y. Antifogging and Icing-Delay Properties of Composite Micro- and Nanostructured Surfaces. ACS Appl. Mater. Interfaces 2014, 6, 3963−3968. (16) Meuler, A. J.; McKinley, G. H.; Cohen, R. E. Exploiting Topographical Texture to Impart Icephobicity. ACS Nano 2010, 4, 7048−7052. (17) Ruan, M.; Li, W.; Wang, B.; Deng, B.; Ma, F.; Yu, Z. Preparation and Anti-Icing Behavior of Superhydrophobic Surfaces on Aluminum Alloy Substrates. Langmuir 2013, 29, 8482−8491. (18) Shen, Y.; Tao, J.; Tao, H.; Chen, S.; Pan, L.; Wang, T. Superhydrophobic Ti6Al4V Surfaces with Regular Array Patterns for Anti-Icing Applications. RSC Adv. 2015, 5, 32813−32818. (19) He, M.; Li, H.; Wang, J.; Song, Y. Superhydrophobic Surface at Low Surface Temperature. Appl. Phys. Lett. 2011, 98, 093118. (20) He, M.; Zhou, X.; Zeng, X.; Cui, D.; Zhang, Q.; Chen, J.; Li, H.; Wang, J.; Cao, Z.; Song, Y.; et al. Hierarchically Structured Porous Aluminum Surfaces for High-Efficient Removal of Condensed Water. Soft Matter 2012, 8, 6680−6683. (21) Varanasi, K. K.; Deng, T.; Smith, J. D.; Hsu, M.; Bhate, N. Frost Formation and Ice Adhesion on Superhydrophobic Surfaces. Appl. Phys. Lett. 2010, 97, 234102. (22) Li, K.; Xu, S.; Shi, W.; He, M.; Li, H.; Li, S.; Zhou, X.; Wang, J.; Song, Y. Investigating the Effects of Solid Surfaces on Ice Nucleation. Langmuir 2012, 28, 10749−10754. (23) Chen, J.; Liu, J.; He, M.; Li, K.; Cui, D.; Zhang, Q.; Zeng, X.; Zhang, Y.; Wang, J.; Song, Y. Superhydrophobic Surfaces Cannot Reduce Ice Adhesion. Appl. Phys. Lett. 2012, 101, 111603. (24) Lv, J.; Song, Y.; Jiang, L.; Wang, J. Bio-Inspired Strategies for Anti-Icing. ACS Nano 2014, 8, 3152−3169. (25) Nosonovsky, M.; Hejazi, V. Why Superhydrophobic Surfaces Are Not Always Icephobic. ACS Nano 2012, 6, 8488−8491. G
DOI: 10.1021/acs.jpcc.5b12298 J. Phys. Chem. C XXXX, XXX, XXX−XXX
