Electron-induced wettability modification

Abstract

The pioneering works by Lippmann [Ann. Chim. Phys. 5, 494 (1875)] and Frumkin [Actual. Sci. Ind. 373, 5 (1936)] reported on electrowetting phenomenon. It was shown that electric potential, applied to an interface between a conducting liquid droplet and solid surface, strengthened the wetting effect. Here, we describe pronounced decrease of wettability induced by a low-energy electron irradiation. We observe this effect in many materials of different origins. The proposed theory of this phenomenon explains the found growth of the hydrophobicity under an electron irradiation by decreasing solid/liquid and solid/vapor interfacial free energies, when reduction of the latter is always higher. This theory considers the droplet shape dependence on the incident electron charge density and energy of the incident electrons, as well as on the liquid and solid origins. The results of calculations are in a good agreement with the experimental data obtained for water droplet on amorphous silicon dioxide. The effect of the decrease of the wettability, induced by an electron irradiation at low incident charge, is completely reversible after subjection of the electron-irradiated material to ultraviolet illumination, which restores its initial wettability state.