An empirical model for sorption by glassy polymers: An assessment of thermodynamic parameters

A new fitting model for sorption by glassy polymers is suggested based on the Flory-Huggins (FH) equation with a composite formula for the FH interaction parameter, chi, which is applicable if sorption experimental data shows a single-maximum variation of the FH parameter. Namely, a power-like and a linear approximation is assumed for chi(phi(1)), as a function of solvent volume fraction phi(1), before and after the point of its maximum. After determining the maximum point from a direct inspection of the sorption data, the three fitting parameters are evaluated by solving two independent least-square minimization problems. Several sorption studies of biopolymers taken from the literature show that the endset of the glass transition region is correlated with the position of the maximum of the FH interaction parameter. Based on this hypothesis and the Vrentas-Vrentas model for sorption of glassy polymers, a theoretical framework for the glass transition analysis is developed. In particular, the solvent-induced glass transition temperature variation can be estimated from the sorption isotherm as a function of the solvent content corresponding to temperatures above the temperature of sorption.

Automated summary

A new fitting model for sorption by glassy polymers is proposed based on the Flory-Huggins equation with a composite formula for the interaction parameter chi. The study shows a correlation between the endpoint of the glass transition region and the position of the maximum of the interaction parameter, providing a theoretical framework for glass transition analysis. Through the analysis, the solvent-induced glass transition temperature variation can be estimated from the sorption isotherm.