Electro-Wetting Behavior of Sodium Chloride Aqueous Solution on Hydrophobic Surfaces of Stainless Steel and Its Influence on Polarization

Abstract

Hydrophobic polyethylene (PE) and perfluorodecyltriethoxysilane (PFDS) were deposited on stainless steels and the contact angle of aqueous NaCl solution on these surfaces was measured before and after applying different currents through a Pt wire. The polarization curves on some surfaces were measured and their relationship to electro-wetting behaviors was determined. Negative rather than positive current greatly reduced the contact angles on both the plane surface of polished SUS304 steel and the rough surface of sputter-etched SUS316 steel (SUS316SE), which were deposited with PE and PFDS, respectively. On rough surfaces, the negative current-induced reduction in contact angle was greater on SUS316SE-PE than on SUS316SE-PFDS specimens. Prior cathode polarization reduced the pitting potential on SUS316SE-PE specimens, but had no effect on 316SE-PFDS specimens. This difference was likely related to the difference in solution invasion into the root of protrusions, from which chromium was depleted by sputter etching.