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REACTION INDUCED PHASE-SEPARATION CONTROLLED BY MOLECULAR TOPOLOGY

by KULKARNI, AMIT S

Abstract (Summary)
Phase-separation can result in the formation of self-assembling structures in networks induced by crosslinking reactions. Vinyl and hydroxyl end-functionalized poly(dimethyl siloxane) (PDMS) chains were employed for the synthesis of these networks using a tetra-functional crosslinking agent. It was found that at a very high molar fraction (approaching 1) of the low molecular weight component, approximately 50% by volume; it was possible to induce composition fluctuations in the system that resulted in phase-separation via spinodal decomposition. Time resolved small angle light scattering (SALS) and optical microscopy were used to determine the character and kinetics of phase-separation and to compare and contrast with the spinodal decomposition of simple blends. A vinyl-terminated system resulted in the formation of interconnected bicontinuous morphology reminiscent of early-stage spinodal decomposition (SD). The morphology obtained by SD was found to be “locked-in”, possibly due to network formation. Late-stage phase ripening was prevented by gelation. Surprisingly, a hydroxyl, end-terminated system was found to display different behavior with simultaneously nucleated close to monodisperse spherical domains. The difference in the mechanisms of phase-separation is believed to arise from the different reaction mechanisms of the two systems with an addition mechanism in the vinyl end-terminated system and a condensation process in the hydroxyl end-terminated system. The reaction mechanism dictates the effective quench depth in the system, which leads to different mechanisms of phase-separation in the two systems. The effect of differences in branch topology, on the phase-separation process has been investigated.
Bibliographical Information:

Advisor:

School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:phase separation pdms networks

ISBN:

Date of Publication:01/01/2005

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