Wetting dynamics of colloidal dispersions on agar gel surfaces

The effects of silica particle addition on the wetting velocity on flat and fractal agar gel surfaces were analyzed along with the applicability of such particles for controlling the wetting dynamics of water. The contact angles (θD) of the colloidal dispersions obeyed the power law, i.e., θD ∝ t−x, where t is time and x is a constant. Wetting was inhibited by the addition of a suitable amount of 20-nm-diameter silica particles. Specifically, the exponent x reached a minimum value for a silica composition of 0.1 wt%. However, such inhibition effects were not observed upon the addition of silica particles with diameters of 100, 550, and, 1000 nm. The mechanism of the inhibition of the liquid wetting on gel surfaces may be attributed to a slight increase in local viscosity around the contact line during wetting.