NMR Approach to the Swelling Process of PDMS Networks and Silica-Filled Siloxanes
This work deals with the NMR observation of the progressive swelling of siloxane systems. Gels re suiting from covalent crosslinks, on the one hand, and network-like structures formed from silica-filled siloxane, on the other hand, were examined. The transverse magnetization of protons was used to probe the unfolding mechanism of elementary chains. The residual energy of spin—spin interactions governing the magnetization dynamics was found to obey static scaling laws upon variation of the solvent concentration. In calibrated gels, these properties reflect both a packing condition and screening effects due to trapped entanglements, whereas neither any affine property nor a packing condition could account for scaling properties observed in silica-filled siloxane systems.
The spin—lattice relaxation rate was found to be independent of the silica concentration, on the one hand, and of the polymer weight fraction w2 (for w2 < 0·5), on the other hand. These two results were assumed to give evidence for the presence of dynamic screening domains, analogous to those existing in any entangled chain solution.
KeywordsRelaxation Rate Residual Energy Transverse Magnetization Chain Segment Silica Concentration
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