Photo-Induced Stick-Slip on Super-Hydrophilic Semiconductor Surfaces

Abstract

The time and relative humidity dependencies of photo-induced super-hydrophilicity on m-TiO2 films have been evaluated through the spreading of a sessile water drop on a UV- illuminated surface. Results obtained at 100% RH show that drops on m-TiO2 exhibit a photo-induced stick-slip behavior, the first time such an effect has been observed. The potential energy barrier U due to the surface inhomogeneities that oppose the onset of movement of the triple line has been obtained as a function of illumination time, also for the first time. U is found to decrease with time, a phenomenon attributed to the influence of the photo-generation of Ti-OH groups on those inhomogeneities affected by surface hydrophilicity.