Preparation and properties evaluation of PDMS Colloidal Silica composites

Abstract

The present research work focuses on the preparation and the characterization of poly(dimethyl)siloxane (PDMS) ? colloidal silica (CS) composites. Various parameters such as the size of CS particles, the loading of CS in the composite, the dispersing aid with which CS particles are dispersed into PDMS, and the surface functionalization of CS are investigated in detail towards obtaining PDMS-CS composites with optimal performance. Both un-functionalized and functionalized CS particles are studied for their composition, thermal and morphological characteristics. The resultant PDMS-CS composites are investigated for their thermal and rheological properties in their un-cure state and for their composition, morphological, optical and mechanical characteristics in their cured state. Even though, the preparation of PDMS composites with high loadings (up to 40 wt %) of un-functionalized ?hydrophilic? CS could be achieved, these composites lack optimal optical and mechanical properties. Though the use of suitable dispersion aid can improve the dispersion of CS to a certain extent, the surface functionalization of CS is required to achieve a good dispersion of CS within PDMS. The preparation of surface functionalized CS (FCS) particles is achieved by treating CS with different functional silanes. Among the different commercial colloidal silica dispersions investigated, CS in water and in methanol dispersions could be functionalized with different mono- and tri-functional silanes efficiently. The surface functionalization of CS in IPA and in MEK dispersions, however, is hampered, due to the partial surface functionalization of CS in these cases. In general, the mechanical properties of the PDMS-CS / FCS composites are found to increase with increasing loading of CS / FCS in the composites.