Chapter 5 - Sorption thermodynamics of low molecular weight compounds in polymers

Abstract

Knowledge of the thermodynamics of sorption of low molecular weight compounds in rubbery and glassy polymers is of great relevance to understanding the physics and dynamics of polymer foaming and for the technological implementation of foaming processes. This chapter is devoted to the illustration of the recent advances in statistical thermodynamics approaches toward the elaboration of a theoretical framework aimed at the description of sorption thermodynamics of small molecules in polymers, addressing also systems that involve specific intra- and intermolecular interactions. In particular, the attention is focused on sorption models rooted on Equation of State theories. Notably, the models discussed here are structured to specifically account for nonrandom distribution of molecular species and for dealing with several kinds of specific interactions, addressing both for the case of rubbery polymers and of out-of-equilibrium glassy polymers. Moreover, a description of the experimental approaches devoted to the measurement of sorption isotherms is provided. Several kinds of experimental methodologies aimed at the description of sorption in polymers are described with attention also to the molecular-level characterization of the polymer-penetrant systems provided by vibrational spectroscopy (FTIR, Raman), which allows for the development of in situ, time-resolved measurements. Sorption thermodynamics in polymers is examined here considering the contact of polymer with a penetrant in a state of a subcritical vapor, of a supercritical fluid, or of a gas.