Effects of surface roughness on wettability of solid surfaces

Transcript

1 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 μm θ γ LV γ SV γ SL Young-Dupre 1 γ LV cos θ e = γ SV γ SL (1) ( Corresponding author : Department of Applied Chemistry, Faculty of Engineering, Shibaura Institute of Technology, 3-7-5, Toyosu, Koto-ku, Tokyo , Japan 115

2 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

3 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 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

5 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 nm EW cos θ V 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= η) 1 (8) Garimella Cassie-Baxter Wenzel r f r Wenzel Cassie-Baxter 50 McCarthy Extrand Bhushan McCarthy Extrand Wenzel Cassie-Baxter 119

6 [1],,, No.447, (2008). [2],,, 57, (2008). [3] S. Imabayashi, N. Gon, T. Sasaki, D. Hobara, and T. Kakiuchi, "Effect of Nanometer-scale Phase Separation on Wetting of Binary Self-assembled Thiol Monolayers on Au(111)," Langmuir, 14, (1998). [4] L. Gao, T. J. McCarthy, How Wenzel and Cassie Were Wrong, Langmuir, 23, (2007). [5] R. N. Wenzel, Resistance of solid surfaces to wetting by water, Ind. Eng. Chem., 28, (1936). [6] A. B. D. Cassie and S. Baxter, Wettability of porous surfaces, Trans. Faraday Soc., 40, (1944). [7] D. M. Spori, T. Drobek, S. Zürcher, M. Ochsner, C. Sprecher, A. Mühlebach, N. D. Spencer, Beyond the Lotus Effect: Roughness In uences on Wetting over a Wide Surface-Energy Range, Langmuir, 24, (2008). [8] N. A. Patankar, On the Modeling of Hydrophobic Contact Angles on Rough Surfaces, Langmuir, 19, (2003). [9] B. He, N. A. Patankar, and J. Lee, Multiple Equilibrium Droplet Shapes and Design Criterion for Rough Hydrophobic Surfaces, Langmuir, 19, (2003). [10] S. Brandon, N. Haimovich, E. Yeger, and A. Marmur, Partial wetting of chemically patterned surfaces: The effect of drop size, J. Colloid Interface Sci., 263, (2003). [11] N. A. Patankar, Transition between Superhydrophobic States on Rough Surfaces, Langmuir, 20, (2004). [12] Q. S. Zheng, Y. Yu, Z. H. Zhao, Effects of Hydraulic Pressure on the Stability and Transition of Wetting Modes of Superhydrophobic Surfaces, Langmuir, 21, (2005). [13] A. Marmur, Wetting on Hydrophobic Rough Surfaces: To Be Heterogeneous or Not To Be?, Langmuir, 19, (2003). [14] E. Bormashenko, Y. Bormashenko, T. Stein, G. Whyman, R. Pogreb, Z. Barkay, Environmental Scanning Electron Microscopy Study of the Fine Structure of the Triple Line and Cassie-Wenzel Wetting Transition for Sessile Drops Deposited on Rough Polymer Substrates, Langmuir, 23, (2007). [15] M. Nosonovsky, B. Bhushan, Patterned Nonadhesive Surfaces: Superhydrophobicity and Wetting Regime Transitions, Langmuir, 24, (2008). [16] A. Marmur, From Hygrophilic to Superhygrophobic: Theoretical Conditions for Making High-Contact-Angle Surfaces from Low-Contact-Angle Materials, Langmuir, 24, (2008). [17] X. M. Li, T. He, M. Crego-Calama, D. N. Reinhoudt, Conversion of a Metastable Superhydrophobic Surface to an Ultraphobic Surface, Langmuir, 24, (2008). [18] V. Bahadur and S. V. Garimella, Electrowetting-Based Control of Droplet Transition and Morphology on Arti cially Microstructured Surfaces, Langmuir, 24, 120

7 (2008) [19] D. L. Herbertson, C. R. Evans, N. J. Shirtcliffe, G. McHale, M. I. Newton, Electrowetting on superhydrophobic SU-8 patterned surfaces, Sens. Actuators A, , (2006). [20] T. N. Krupenkin, J. A. Taylor, T. M. Schneider, and S. Yang, From Rolling Ball to Complete Wetting: The Dynamic Tuning of Liquids on Nanostructured Surfaces, Langmuir, 20, (2004). [21] L. Zhu, J. Xu, Y. Xiu, Y. Sun, D. W. Hess, and C.-P. Wong, Electrowetting of Aligned Carbon Nanotube Films, J. Phys. Chem. B, 110, (2006). [22] M. S. Dhindsa, N. R. Smith, J. Heikenfeld, P. D. Rack, J. D. Fowlkes, M. J. Doktycz, A. V. Melechko, and M. L. Simpson, Reversible Electrowetting of Vertically Aligned Superhydrophobic Carbon Nanofibers, Langmuir, 22, (2006). [23] Z. Wang, Y. Ou, T.-M. Lu, and N. Koratkar, Wetting and Electrowetting Properties of Carbon Nanotube Templated Parylene Films, J. Phys. Chem. B, 111, (2007). [24] T. N. Krupenkin, J. A. Taylor, E. N. Wang, P. Kolodner, M. Hodes, T. R. Salamon, Reversible Wetting-Dewetting Transitions on Electrically Tunable Superhydrophobic Nanostructured Surfaces, Langmuir, 23, (2007). [25] N. Verplanck, E. Galopin, J.-C. Camart, V. Thomy, Reversible Electrowetting on Superhydrophobic Silicon Nanowires,, Nano Lett., 7, (2007). [26] C. W. Extrand, Contact Angles and Hysteresis on Surfaces with Chemically Heterogeneous Islands, Langmuir, 19, (2003). 121