Dielectric relaxation and elasticity during polymerization.
A molecular kinetics-elasticity relation has been investigated by using real time dielectric spectroscopy of a diepoxide-triamine liquid mixture polymerizing at 298 K. As the liquid polymerized, the dielectric relaxation time tau increased linearly with the exponential of the known value of the instantaneous shear modulus G(infinity), in agreement with the elastic model for viscous flow but without the effect of temperature. Thus the structure-dependent effect on the Brownian motions are separated from the temperature-dependent effect. In this time-dependent process, increase in G(infinity) may be compensated by an increase in T, thereby keeping G(infinity) and tau constant. In the potential energy landscape paradigm, a polymerizing liquid's state point, like a normal liquid's on cooling, continuously shifts to deeper and lower energy minima of higher curvature, but the shift occurs irreversibly to other parts of the total energy landscape, thus adding a reaction coordinate to the landscape. A minimum in the energy landscape corresponding to a structure formed by polymerization may be identical to a minimum in another landscape corresponding to another structure.
Venkateshan
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Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario L8S 4L7, Canada.
Johari
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