title: Wetting and wetting transitions on copper-based super-hydrophobic surfaces.
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.
authors.affiliation: School of Biomedical and Natural Sciences, The Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom. neil.shirtcliffe@ntu.ac.uk
authors.forename: N J
authors.initials: NJ
authors.lastname: Shirtcliffe
authors.forename: G
authors.initials: G
authors.lastname: McHale
authors.forename: M I
authors.initials: MI
authors.lastname: Newton
authors.forename: C C
authors.initials: CC
authors.lastname: Perry