STUDIES OF SURFACE MODIFICATION OF SOLIDS .4. IMMERSIONAL HEATS AND INFRARED-SPECTRA OF ORGANOSILANE-TREATED SILICA

The surface of silica was treated with trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDS) respectively and the immersional heat into water, adsorption capacity for water vapor and infrared absorption spectra were measured. TMCS reacts with freely vibrating silanols while HMDS also reacts with other silanols. By treatment with silane, the silica surface is covered by the trimethylsilyl group, a maximum amount of which attains 1 meq/g (3 groups/nm**2). As the amount of the trimethylsilyl group on silica increases, the immersional heat of silica into water decreases and attains a constant value of about 25 erg/cm**2, which is the typical value for a hydrophobic surface. The interaction of the trimethylsilyl group with water is weak, therefore the adsorptive capacity for water vapor is lessened remarkably by treatment with silane.