Journal of Materials Science, Vol.52, No.1, 595-604, 2017
Droplet viscosity effects on dynamic hydrophobicity of a solid-liquid bulk composite prepared from porous glass
Hydrophobic porous glass plates were prepared by coating a fluorosilane (FAS17) onto a commercial porous glass (average pore size, approx. 1 mu m). Based on the spreading coefficients from interface energies, we prepared solid-liquid bulk composites (SLBC) without direct contact between the solid surface and liquid droplet by impregnation of silicone oil into the silane-coated porous glass. Impregnating the oil into the porous glass decreased both the sliding angle (ca. 20A degrees -> ca. 5A degrees) and contact angle (ca. 135A degrees -> ca. 100A degrees). The sliding velocity of the liquid droplets on the SLBC decreased when the droplet viscosity was increased using a water-glycerin mixture. Analysis by particle image velocimetry revealed that increasing the viscosity remarkably decreases the slipping motion and increases the contribution of rolling. Results suggest that the practical internal fluidity of the droplets during sliding on the SLBC is governed by the combination of the droplet liquid and the oil impregnated into the porous media.