Structural Transitions in Glassy Atactic Polystyrene Using Transition-State Theory

Transition pathways on the energy landscape of atactic polystyrene (aPS) glassy specimens are probed below its glass-transition temperature. Each these transitions is considered an elementary structural relaxation event, whose corresponding rate constant calculated by applying multidimensional transition-state theory. Initially, a wide spectrum first-order saddle points surrounding local minima discovered stabilized hybrid eigenmode-following method. Then, (minimal-energy) “reaction paths” to adjacent constructed quadratic descent The heights free energy, potential and entropy barriers estimated for every connected triplet transition state minima. resulting distribution asymmetric extremely broad, extending very high barrier (over 50 kBT); constants extends over 30 orders magnitude, with well-defined peaks at time scales subglass relaxations polystyrene. Analysis curvature along reaction paths reveals multitude different rearrangement mechanisms; some them bearing multiple distinct phases. Finally, connections theoretical models glass phenomenology allows prediction, based first-principles, “ideal” temperature entering Vogel–Fulcher–Tammann (VFT) equation describing super-Arrhenius dependence dynamics. Our predictions VFT in favorable agreement available experimental literature data systems similar molecular weight under same conditions.