Wetting and wetting transitions on copper-based super-hydrophobic surfaces |
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Authors: | Shirtcliffe N J McHale G Newton M I Perry C C |
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Institution: | School of Biomedical and Natural Sciences, The Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom. neil.shirtcliffe@ntu.ac.uk |
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Abstract: | Rough and patterned copper surfaces were produced using etching and, separately, using electrodeposition. In both of these approaches the roughness can be varied in a controlled manner and, when hydrophobized, these surfaces show contact angles that increase with increasing roughness to above 160 degrees . We show transitions from a Wenzel mode, whereby the liquid follows the contours of the copper surface, to a Cassie-Baxter mode, whereby the liquid bridges between features on the surface. Measured contact angles on etched samples could be modeled quantitatively to within a few degrees by the Wenzel and Cassie-Baxter equations. The contact angle hysteresis on these surfaces initially increased and then decreased as the contact angle increased. The maximum occurred at a surface area where the equilibrium contact angle would suggest that a substantial proportion of the surface area was bridged. |
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