WETTING DYNAMICS STUDIES ON SILICA SURFACES OF VARIED HYDROPHOBICITY

The kinetics of movement of the three-phase line of contact (tplc) have been studied as nitrogen displaces water from hydrophobic, smooth silica surfaces. The silica surfaces were quantitatively hydrophobized with trimethylchlorosilane, tert-butyldimethylchlorosilane and long-chain alcohols over a range of contact angles. Both forced and spontaneous movement were studied by high-speed photography. Neither the geometry of the experiment nor variations in electrical double-layer forces had any detectable influence on the results obtained. The difference between the cosines of the dynamic and static water receding contact angles, DELTA cos, is related to the velocity of the tplc, V, by DELTA cos = (2 s m-1)V + B for 20 x 10(-3) m s-1 < V < 100 x 10(-3) m s-1, where B may reflect molecular reorientation changes at the solid-liquid and solid-vapor interfaces.