Abrupt Change on the Wettability of Vapor-Deposited Thin Silane Film Upon Evaporative Drying and Annealing

The effects of evaporative drying and annealing processes on the wettability and morphology characteristics of vapordeposited self-assembled 1H,1H,2H,2H-perfluorooctyltrichlorosilane (CF3(CF2)5(CH2)2SiCl3) (FOTS) thin film on glass substrate were investigated. Removal and desorption of FOTS were found to occur during alcohol rinsing/drying and low temperature annealing at 80°C, as evidenced by the increase in the FOTS oxygen/carbon (O/C) elemental ratio based on X-ray photoelectron spectroscopy study. The surfaces of FOTS thin film were reconstructed and a mechanism was proposed that accounts for the effect of solvent penetration through defect sites of FOTS thin film. The resulting topography increased the water static contact angle by as much as 26° whereas the contact angle hysteresis remained unchanged. A concurrent increase in water dynamic contact angles of 14°was also observed. In addition to the topography effect, the increase in contact angles was also attributed to the changes of the proportions of hydrophobic and hydrophilic area fraction (static and dynamic) and pinning effect (dynamic).