Combined Description of Pressure-Volume-Temperature and Dielectric Relaxation of Several Polymeric and Low-Molecular-Weight Organic Glass-Formers using 'SL-TS2' Mean-Field Approach

TL;DR

This paper demonstrates that the 'SL-TS2' mean-field model can accurately describe and predict the pressure, volume, temperature, and dielectric relaxation behavior of various polymers and organic glass formers, aligning with thermodynamical scaling laws.

Contribution

The study extends the 'SL-TS2' model to simultaneously fit dielectric relaxation and PVT data for multiple materials, enabling pressure-dependent predictions based on scaling laws.

Findings

Good agreement between model and experimental data for relaxation times and volumes.

Validation of thermodynamical scaling across different materials.

Model's potential to predict behavior under elevated pressures.

Abstract

We apply our recently-developed mean-field 'SL-TS2' (two-state Sanchez-Lacombe) model to simultaneously describe dielectric alpha-relaxation time and pressure-volume-temperature (PVT) data in four polymers (polystyrene, poly(methylmethacrylate), poly(vinyl acetate) and poly(cyclohexane methyl acrylate)) and four organic molecular glass formers (ortho-terphenyl, glycerol, PCB-62, and PDE). Previously, it has been shown that for all eight materials, the Casalini-Roland thermodynamical scaling, /tau_{/alpha} = f(TV_{sp}^{/gamma}) (where T is temperature and V_{sp} is specific volume), (Casalini, R.; Roland, C. M. Phys. Rev. Lett. 2014, 113 (8), 85701), is satisfied. It has also been previously shown that the same scaling emerges naturally (for sufficiently low pressures) within the 'SL-TS2' framework (Ginzburg, V. V. Soft Matter 2021, 17, 9094). Here, we fit the ambient pressure curves for the relaxation time and the specific volume as functions of temperature for the eight materials and observe a good agreement between theory and experiment. We then use the Casalini-Roland scaling to convert those results into 'master curves', thus enabling predictions of relaxation times and specific volumes at elevated pressures. The proposed approach can be used to describe other glass-forming materials, both low-molecular-weight and polymeric.