Wetting Properties of the Multiscaled Nanostructured Polymer and Metallic Superhydrophobic Surfaces Edward Bormashenko,* Tamir Stein, Gene Whyman, Yelena Bormashenko, and Roman Pogreb The College of Judea and Samaria, the Research Institute, 44837, Ariel, Israel ReceiVed June 6, 2006. In Final Form: September 18, 2006 A superhydrophobic surface is produced from industrial grade polymer materials. The surface comprises partly disordered triple-scaled arrays of polyvinylidene fluoride (PVDF) globules. An inherently superhydrophobic metallic surface is produced with polymer template. The mathematical model based on the Cassie-Baxter hypothesis of air trapping under a water drop is built, which gives the apparent contact angle on the manifold-scaled interface. The presence of several scales itself is not a sufficient condition of hydrophobicity of inherently wettable surfaces. The geometrical features favoring the increase of the vapor-water interface fraction are necessary for this phenomenon. 1. Introduction Wetting of textured surface has been studied intensively in the past decade. 1-25 Although the main theoretical approaches to the wetting of highly developed relieves were developed by Cassie and Wenzel 50 years ago, the problem still turns to be attractive to investigators. According to the Cassie model, air can remain trapped below the drop, forming “air pockets”. Thus, hydro- phobicity is strengthened because the drop sits partially on the air. On the other hand, according to the Wenzel model, the roughness increases the surface area of the solid, which also geometrically modifies hydrophobicity. 1 It is conventional to relate so-called moderate hydrophobicity to the Wenzel regime, whereas the Cassie scenario results in strong water-repellent surface properties. However, the Cassie regime has been reported recently for slightly hydrophobic interfaces; moreover, coexist- ence of Cassie and Wenzel regimes at the same surfaces has been reported. 4,24 Lack of the reproducible experimental data in the field has to be emphasized. The phenomenon of superhydrophobicity when apparent contact angle becomes close to 180° was reported recently by different groups. 2,3,8 Various sophisticated techniques (UV, soft lithography, 11 and temperature-directed capillary molding 24 ) and materials (perfluoroacrylates 4 and alkylketene dimers 10 ) were applied for manufacturing super-water-repellent surfaces. Su- perhydrophobic surfaces are also found in nature. 9,12 The biological expedience of the phenomenon, called the lotus effect, consists of the possibility of self-cleaning of plant leaves because of the rolling of drops without water spreading on the leaf surface. 9,12 The underlying physical problem was how hydro- phobicity can develop on materials which are partially wettable. 9 This phenomenon has been explained by forming the large water- air interface under a water droplet in consequence of the air trapping in pockets of a highly textured substrate. Since the surface energy of the water-air interface is large, the droplet tends to decrease the underlying area increasing the contact angle. Despite significant experimental and theoretical efforts, reproducible inexpensive manufacturing of superhydrophobic surfaces remains problematic. We report triple-scaled superhy- drophobic surfaces manufactured with industrial grade polyvi- nylidene fluoride (PVDF) particles, dispersed at the polyethylene substrate. PVDF is inherently a hydrophilic material; 14 its calculated contact angle equals 80-86°, and a measured value on our nanometrically flat samples was 75°. Surfaces, prepared according to our process and comprising nanometrically scaled PVDF beads, demonstrated apparent contact angle as high as 160° (see Figure 1a). Among the recent achievements, metallic superhydrophobic surfaces attract significant attention. Metallic surfaces are well- known as “high-energy interfaces”, for which the chemical binding is about 1 eV, and on which nearly every liquid spreads. 1 Superhydrophobic metallic surfaces are usually obtained with a monolayer of n-dodecanthiol assembled on textured metallic surfaces. 15-17 We will demonstrate in our paper that it is possible to form inherently hydrophobic metallic interface, when the later is micrometrically textured, with a contact angle as high as 150°, Figure 1b. * Author to whom correspondence should be addressed. E-mail: Edward@yosh.ac.il. (1) de Gennes, P. G.; Brochard-Wyart, F.; Que¨re¨, D. Capillarity and Wetting Phenomena; Springer: Berlin, 2003. (2) Gao, L.; McCarthy, Th. J. Langmuir 2006, 22, 2966-2967. (3) Vogelaar, L.; Lammertink, R. G. H.; Wessling, M. Langmuir 2006, 22, 3125-3130. (4) Lafuma, A.; Que´re´, D. Nat. Mater. 2003, 2, 457-460. (5) Bico, J.; Thiele, U.; Que´re´, D. Colloids Surf., A 2002, 206, 41-46. (6) Sun, M. H.; Luo, C. X.; Xu, L. 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