PHOTOPHYSICAL STUDIES OF PROBES BOUND TO CROSS-LINK JUNCTIONS IN POLY(DIMETHYL SILOXANE) ELASTOMERS AND NANOCOMPOSITES

Naphthalene and dansyl chromophores are covalently attached to trifunc tional cross-link junctions in poly(dimethyl siloxane) elastomers. Pho tophysical measurements are subsequently used to monitor the junction dynamics in unfilled elastomers and the local junction environment in nanocomposites prepared by sol-gel in-situ precipitation techniques. T ransient fluorescence anisotropy measurements of the naphthalene chrom ophore are interpreted in terms of a fast, partial reorientation withi n a restricted cone and a slow, complete reorientation driven by coope rative motions of larger chain segments connected to the cross-link. S teady state fluorescence measurements of the dansyl chromophore in unf illed elastomers and in silica-containing nanocomposites suggest the e xistence of two populations of chromophores: one that is tightly immob ilized through interactions with inorganic domains and a second that i s free to move within the elastomeric domain.