Ultrasonic Excitation Induced Wenzel to Cassie Transition

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Conference Proceeding

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Wetting on textured solids has gained much attention in the past decade due to increasing interest in artificial superhydrophobic surfaces. (Bahadur & Garimella, 2007; Boreyko & Chen, 2009; Forsberg, Nikolajeff, & Karlsson, 2011; Heikenfeld & Dhindsa, 2008) On textured surfaces, the wetting liquid can be in either the Cassie–Baxter state, which the liquid does not fill the surface texture; or the Wenzel state, which the liquid completely wets the surface and fills the recesses. For a hydrophobic micro-scale rough surface, the Cassie state is usually a more favorable state since it requires less energy. However, due to contact angle hysteresis, the Wenzel state can also be meta-stable. By controlling the roughness of the texture and initial droplet position, both Cassie and Wenzel states can be stable simultaneously. (Koishi, Yasuoka, Fujikawa, Ebisuzaki, & Xiao, 2009) However, with the proper energy input, the droplets can be induced to transition between states. While multiple methods have been developed to switch from Cassie to Wenzel states (Bormashenko, Pogreb, Whyman, & Erlich, 2007; Krupenkin et al., 2007; Kumari & Garimella, 2011; Ran, Ding, Liu, Deng, & Hou, 2008), it is much more difficult to switch from the Wenzel state to the Cassie state. Wenzel-Cassie transitions have been achieved by changing the surface structure to destabilize the Wenzel state (Krupenkin et al., 2007)(Ran et al., 2008) or by changing the ambient fluid (Dhindsa et al., 2006).

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ASME 2011 International Mechanical Engineering Congress and Exposition, v. 11, p. 639-641, art. IMECE2011-64391