Combined description of polymer <i>PVT</i> and relaxation data using a dynamic "SL-TS2" mean-field lattice model.
basic_science · Level V
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- Also identified by DOI 10.1039/d1sm00953b.
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Abstract
We develop a combined model to describe the pressure-volume-temperature (<i>PVT</i>) thermodynamics and the <i>α</i>- and <i>β</i>-relaxation time dynamics in glass-forming amorphous materials. The <i>PVT</i> results are described using a two-state modification of the Sanchez-Lacombe equation of state (SL-EoS). The minimization of the Sanchez-Lacombe free energy expression allows one to calculate the density (or specific volume) and the "solid fraction" as a function of temperature and pressure. The solid fraction, <i>ψ</i>(<i>T</i>,<i>P</i>), is then substituted into the TS2 mean-field model (V. V. Ginzburg, <i>Soft Matter</i>, 2020, <b>16</b>, 810), and the equilibrium relaxation times and the glass transition temperature are calculated. Finally, we use a dynamic model of a Tool-Narayanaswami-Moynihan (TNM)-type to describe the density relaxation as a function of the cooling rate. We applied the new framework to describe experimental data for polystyrene and poly(methylmethacrylate) and found a good qualitative and quantitative agreement.