(397a) Accounting for Excitations Allows for Liquid Phase Dynamics Predictions

While simple predictive frameworks for transport in gases and solids have long existed, the same cannot be said for amorphous condensed matter, which includes liquids, glasses, and many biological and synthetic polymers. One difficulty in amorphous condensed matter model development is the dynamic heterogeneity materials in this state experience. Treatment of these materials as discontinuous matter has been successful in providing a route for exploration, with one example being the potential energy landscape (PEL) concept developed by Goldstein.

One notable feature of the PEL framework is inherent states (IS) which are locally low energy conformations of clusters of molecules. While in an IS, molecules are not static, but rather move around and explore this conformation, resulting in regions of the material that have locally high and low density. In certain cases, these low-density regions result in discrete molecular rearrangements which allow molecules to move outside of the IS and explore a new local energy minimum. These density fluctuations that result in molecules “hopping” into a new conformation are referred to as “excitations”.

For the first time, Cicerone, using neutron scattering, has developed an approach for measuring hops and excitations in real liquid systems¹. The present work describes the connection between macroscopic thermodynamic parameters, such as enthalpy and entropy of melting, and hops – the most fundamental transport process in the liquid phase. This work also demonstrates our capabilities to predict relaxation behavior of liquid materials from these thermodynamic parameters. The real liquids systems used for this work are propylene carbonate, propylene glycol, glycerol, and sorbitol. With this work, the prospects of developing simple models to capture elusive liquid behavior become promising.

1. Cicerone et al., arXiv:2201.12593 [cond-mat.soft] (2022)