DEPENDENCE OF MOLECULAR-WEIGHT OF GRAFTING POLYMER ON DISPERSIBILITY OF TIO2 PARTICLES IN POLY(DIMETHYLSILOXANE)

The effect of the molecular weight of the grafting polymer (a derivative of poly(dimethylsiloxane)) on the dispersibility of TiO2 particles coated with SiO2 in poly(dimethylsiloxane) has been investigated. It has been found that there exists an optimal molecular weight for their dispersibility determined from the time dependence of the turbidity of suspensions. The pair interaction energy, which was assumed to be the sum of van der Waals interaction energy, entropic repulsive energy, and bridging adsorption energy through the grafting polymer, was calculated. Comparison of the experimental and calculated results suggested the following. In the dispersion system containing particles grafted with small-molecular-weight (<800) polymer, the aggregation is accelerated by a deep secondary potential minimum resulting from the van der Waals energy with a more long-range character which overwhelms the entropic repulsion energy. On the other hand, in the dispersion system containing particles having a larger-molecular-weight (>3780) polymer, the bridging adsorption is chiefly responsible for the aggregation. It was concluded that these results lead to the presence of the optimal molecular weight of the grafting polymer in the dispersibility. © 1993 Academic Press, Inc.