Effects of surface roughness on wettability of solid surfaces Shin-ichiro Imabayashi Recent papers discussing the effect of surface roughness on wettability of solid surfaces are reviewed. Wenzel s and Cassie-Baxter s wetting models, factors determining the relative stability of the wetting models, and the control of the surface wettability by electrowetting are introduced. γ (N m -1 = J m -2 ) Lotus effect μm 200 1000 μm θ γ LV γ SV γ SL Young-Dupre 1 γ LV cos θ e = γ SV γ SL (1) ( 135-8548 3-7-5 Corresponding author : Department of Applied Chemistry, Faculty of Engineering, Shibaura Institute of Technology, 3-7-5, Toyosu, Koto-ku, Tokyo 135-8548, Japan 115
Wenzel Cassie-Baxter Wenzel (2) θ w θ e θ rec < θ e < θ adv r r 1 (2) r cos θ w = r cos θ e = r (γ SV γ SL ) / γ LV (2) f 180 cos θ air = 1 (4) cos θ CB = fr cos θ e + (1-f) cos θ air (3) cos θ CB = f (r cos θ e + 1) 1 (4) f f = 1 Wenzel θ e θ w θ CB Spencer Cos θ e cos θ w (θ CB ) θ e < 120 A θ > 150 Wenzel Cassie-Baxter θ e θ w (θ CB ) Wenzel θ e = θ W = 90 r (a) Wenzel (b), Cassie-Baxter (c) Cassie-Baxter (3) θ CB r 2 Cos θ e cos θ W (θ CB ) 116
B (θ e < 90 ) (θ e > 90 ) Cassie-Baxter f 1 Wenzel Cassie-Baxter θ e 3 Wenzel Cassie-Baxter θ CB θ W θ e θ e θ e Cassie-Baxter Wenzel θ e r f Wenzel, Cassie-Baxter ( ) Cassie-Baxter Wenzel Wenzel Cassie-Baxter Wenzel a b h b / a H / a Cassie-Baxter θ e ~ Wenzel, Cassie-Baxter Cassie-Baxter Wenzel 117
4 γ SL θ e < 90 θ CB > 90 Cassie-Baxter θ e < 90 θ CB > 90 Wenzel Cassie-Baxter Spencer Cos θ e cos θ W (θ CB ) Wenzel Cassie-Baxter θ e < 90 θ C > 90 Cassie-Baxter Wenzel, Cassie-Baxter Patankar Cassie-Baxter Wenzel EW EW V (5) C γ SL (6) μ TAS 118
γ SL (V) = γ SL V=0 1/2 CV 2 (5) cos θ (V) = cos θ V=0 + CV 2 / 2γ LV (6) θ e 5 Cassie-Baxter Cassie-Baxter EW θ e Wenzel Cassie-Baxter 10 100 nm EW cos θ V 2 10 50 V Cassie-Baxter Wenzel Heikenfeld dodecane Kurpenkin (6) Wenzel Cassie-Baxter (7), (8) EW cos θ w (V) = r (cos θ V=0 + η) η = CV 2 / 2γ LV (7) cos θ CB (V) = f (r cos θ V=0 + 1 + η) 1 (8) Garimella Cassie-Baxter Wenzel r f r Wenzel Cassie-Baxter 50 McCarthy Extrand Bhushan McCarthy Extrand Wenzel Cassie-Baxter 119
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