Interdiffusion of Solvent into Glassy Polymer Films: A Molecular Dynamics Study

TL;DR

This study uses molecular dynamics and Monte Carlo simulations to analyze how solvent diffuses into glassy polymers, revealing Fickian behavior with concentration-dependent diffusivity near the glass transition.

Contribution

It provides a detailed comparison of diffusivity from Fick's model and Darken equation, highlighting the influence of polymer state on diffusion behavior.

Findings

Weight gain follows t^{1/2} law indicating Fickian diffusion.

Diffusivity varies strongly with solvent concentration near glass transition.

Good agreement between diffusivity from Fick's model and Darken equation.

Abstract

Large scale molecular dynamics and grand canonical Monte Carlo simulation techniques are used to study the behavior of the interdiffusion of a solvent into an entangled polymer matrix as the state of the polymer changes from a melt to a glass. The weight gain by the polymer increases with time $t$ as $t^{1/2}$ in agreement with Fickian diffusion for all cases studied, although the diffusivity is found to be strongly concentration dependent especially as one approaches the glass transition temperature of the polymer. The diffusivity as a function of solvent concentration determined using the one-dimensional Fick's model of the diffusion equation is compared to the diffusivity calculated using the Darken equation from simulations of equilibrated solvent-polymer solutions. The diffusivity calculated using these two different approaches are in good agreement. The behavior of the diffusivity strongly depends on the state of the polymer and is related to the shape of the solvent concentration profile.