Determination of trimethylchlorosilane modified silica surface properties by adsorption of hexamethyldisiloxane

Fumed silicas are common and convenient fillers for polydimethylsiloxane (PDMS) elastomers. A difficulty encountered is the slow hardening of an uncured PDMS/silica mix during storage. This phenomenon can be suppressed by a controlled partial silylation of the silica surface. Using gas adsorption of hexamethyldisiloxane at 303 K, the residual surface activity of trimethylchlorosilane modified silicas was studied. The main adsorption parameters such as Henry's constant, BET constant, BET surface area and distribution functions of adsorption energies were determined from the isotherms. The variations of the previous quantities with the silica surface coverage by trimethylsiloxy groups will be discussed.