Preparation and properties of poly(dimethyl siloxane)-colloidal silica/functionalized colloidal silica nanocomposites

Aqueous spherical colloidal silica (CS) particles with a diameter of 15 ± 5 nm were modified with three different types of monofunctional silane coupling agents to prepare functionalized colloidal silica (FCS) particles. The effects of the surface chemistry of the FCS were studied as a function of the CS/FCS loading in the poly(dimethyl siloxane) (PDMS) polymer. The prepared PDMS-CS/FCS composites were investigated for their physical properties both in the cured and uncured states. The extent of filler-filler and filler-polymer interactions was found to vary with the type of functionalizing agent used to treat the surface of the CS. The filler-filler interaction appeared to be predominant in the PDMS-CS composites, and improved filler-polymer interaction was indicated in the case of the PDMS-FCS composites. The composites containing CS treated with methyltrimethoxysilane exhibited relatively better optical and mechanical properties compared to the other PDMS-FCS composites. This study highlighted the importance of judiciously choosing functionalizing agents to achieve PDMS-FCS composites with predetermined optical and mechanical properties.