Adsorption of Polydimethylsiloxane on Hydrophilic and Silylated Fumed Silica. Investigations by Differential Scanning Calorimetry

Abstract

Fumed silica is a synthetic amorphous silicon dioxide produced by burning silicon tetrachloride in an oxygen-hydrogen flame. Surface areas range from 50 m2/g up to 400 m2/g. Fumed silica is used as an active filler providing a high performance in reinforcing silicone rubbers. Adsorption interactions of the polydimethylsiloxane (PDMS) chains within the elastomeric network on the filler surface play an important role in the mechanisms of reinforcement. The aim of this paper is to study the impact of surface silylation on the adsorption behavior of PDMS polymers on hydrophilic and silylated surfaces. Differential scanning calorimetry (DSC) was used to monitor the impact of adsorption on the mobility of the PDMS chains. Typical DSC signals, like the glass transition, are observed for only the free polymer, but not for polymer chains adsorbed at the silica surface. The PDMS adsorption capacity of silicas at different degrees of silylation has been determined. On the free silica surface, adsorption results in about four to five layers of immobilised PDMS chain segments.