Segmental Interaction Energy Controls a Wide Range of Material Behavior

In molecular and material modeling, the interaction energy (ε) between segments is a key parameter. Its value is typically specified by connecting experimental thermodynamic behavior, e.g., pressure-volume-temperature (PVT) data, with a model relationship, e.g., a theoretical equation of state (EOS). In this paper, we elevate the practical importance of segmental interaction energies by demonstrating their influence over a surprisingly wide span of behavior, from molecular relaxation and glassification to polymer miscibility. We also quantify an exceptionally strong, direct correlation between ε and the thermal expansion coefficient, which opens opportunities when system data are limited, broadening the scope of thermodynamic characterization to methods such as ellipsometry. Using a variety of experimental data to obtain ε, alongside the EOS prediction for molecular size, we draw bright lines from thermodynamic characterization to predictions for the glass transition temperature, relaxation times associated with the (segmental/structural) α-process, and both activation energies and relaxation times for the small-scale collective motions that enable the newly revealed Slow Arrhenius Process (SAP). The latter is connected to phenomena ranging from stress relaxation and flow to adsorption and crystallization, lipid transfer, and physical aging. We then reverse the path from characterization to prediction by showing that dynamic measurements, specifically on SAP relaxations, can be used to characterize segmental interactions. We demonstrate that the resulting dynamics-derived parameters are effective in making verifiable predictions about polymer miscibility.