Universality of Dynamic and Thermodynamic Behavior of Polymers near their Glass Transition

Abstract: Describing the dynamics and thermodynamics of amorphous materials near the glass transition is a major challenge in soft-matter physics and polymer engineering. Here, we show that the dependence of the dielectric alpha-relaxation time on temperature can be captured by a universal equation with only two independent parameters, Tg and fragility, m. This is similar in spirit to the ideas of van Krevelen and Bicerano, and can be related to the Boyer-Spencer and Simha-Boyer rules for the volumetric thermal expansion via a modified free-volume approach such as Sanchez-Lacombe "Two-state, two-(time)scale" (SL-TS2) theory. The model is compared to experimental data for nine amorphous polymers with varying values of Tg and m, and a good qualitative and quantitative agreement is found. We also derive the relationship between the experimental and computational (high-cooling-rate) Tg, and compare our model prediction for the Tg-shift between the two with the simulation results of Afzal et al., finding a good qualitative and semi-quantitative agreement. The results could serve as a guidance for future simulation studies.