Wetability of sol-gel-derived TiO2 films

TiO2 thin films were deposited on glass substrates by the sol-gel process using spin-coating technique. Three kinds of sol systems were used to produce the films which were then baked at various temperatures. Water contact angles of the films were measured using the tilting plate method. The initial water contact angle of an as-prepared film was < 5<degrees>, and after a certain period of placement it started to increase gradually up to a maximum of 72 degrees. Water adsorption was found to accelerate the increase of the contact angle. Appropriate UV light irradiation could make the high (72 degrees) water contact angle of the film return to the initial value, i.e., < 5<degrees>. Films prepared with DEA-chelated precursors have higher speed of increase in the water contact angle than those prepared with AcAc-chelated precursors or without any chelating agent. AFM images showed that the surface roughness of these films were different, suggesting that the surface roughness is another factor affecting the wettability of the films.