An equation of state (EoS)-based approach to describe gas and vapor solubility in mechanically constrained phases: The case of semicrystalline polymers

The Equation of State (EoS) models, which are rather successful in describing the experimental solubility in molten polymers, often fail to describe the same property in the amorphous phase of the same polymers below Tm (estimated assuming negligible sorption in the crystalline domains).[1] In particular, often the EoS model overestimates the actual solubility measured in the amorphous phase below Tm. Such behavior is rather frequent and cannot be simply attributed to inaccurate estimates of the crystalline fraction. Moreover, such phenomenon is in conflict with the assumption that the crystalline phase does not affect the sorption properties of the amorphous one. Interestingly, the same overestimation of experimental data was observed when calculating the solubility of the amorphous phase with a Montecarlo (MC) algorithm, as it was done by Memari et al. In such work, the authors hypothesized that the amorphous phase, due to the presence of crystals, is subject to an additional pressure which enhances its mass density, and lowers its sorption capacity. The authors also provide estimates of such extra-pressure and constrained density, as well as constrained solubility, by using the MC algorithm. In this work, we consider the same assumption, but we compute the extra-pressure, the constrained density and the solubility of the amorphous polymer phase with computationally inexpensive macroscopic tools.