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Rheology of a polydimethylsiloxane model polymer network near its gel point
Abstract
The rheological behavior of polymers at the gel point (critical gels) is characterized by a power law distribution of relaxation times, large normal stress differences, and physical rupture of molecular network strands. This is demonstrated in a series of well-defined experiments conducted on a model network polymer system consisting of a linear, telechelic, vinyl-terminated polydimethylsiloxane (PDMS) and a four-functional siloxane crosslinker. Stable samples of this model polymer can be prepared at different extents of reaction in the vicinity of the gel point (GP), thereby separating the effects of reaction and flow. The linear viscoelastic constitutive equation (Gel Equation) has been extended to include the effect of finite strains, and has been found to describe the rheological behavior of critical gels extremely well. Large strains have been found to disrupt the network structure of the crosslinking polymer, and introduce a mechanical delay to gelation. As a result, a stable sample can be reduced from a viscoelastic solid to a critical gel, or even to a viscoelastic liquid, depending on the magnitude of the shear strain. This mechanical effect also shifts the value of the relaxation exponent, n, at the gel point towards lower values. The material properties can therefore be controlled by both the chemistry and the processing, to suit the application.
Subject Area
Chemical engineering|Polymer chemistry
Recommended Citation
Venkataraman, Sundar Kilnagar, "Rheology of a polydimethylsiloxane model polymer network near its gel point" (1990). Doctoral Dissertations Available from Proquest. AAI9110227.
https://scholarworks.umass.edu/dissertations/AAI9110227