Tuning pore size and hydrophobicity of macroporous hybrid silica films with high optical transmittance by a non-template route

Abstract

Macroporous silica films with methyl groups grafted on their surface were prepared from polymethylhydrosiloxane (PMHS) and tetraethylorthosilicate (TEOS) without templates. Compared to the conventional template syntheses, this approach has several advantages. First, it avoids the removal of templates, which is sometimes an environmentally unfriendly procedure. Second, it does not require a post-synthesis grafting to form the hybrid structures with methyl groups on the silica surface. Third, the pore size and hydrophobicity (expressed by the water contact angle) of the film can be tuned readily. By adjusting the amount of PMHS used in the synthesis and introducing hexamethyldisilazane (HMDS) we can tune the pore size in a wide range from 50 nm to 500 nm. The hydrophobicity increases substantially as the pore size decreases. Evidently, the reaction mechanism of this synthesis is different from the conventional template synthesis. A tentative mechanism is proposed: the hydrogen gas released from PMHS results in the formation of the macropores in the films. With excellent hydrophobicity, optical transmittance and thermal stability, the obtained silica films have potential applications in the semiconductor industry.