Validation of Shell-like Free Volume Model for Self-Diffusion Coefficients in Polymer-Solvent System with Practical Parameter Determination Method

The shell-like free volume (SLFV) model, which was proposed for predicting the self-diffusion coefficients of solvents in polymer solutions, is validated in this study through a practical parameter determination method. Although the SLFV model requires a value for the molecular surface area of the components in the system, the van der Waals (vdW) surface area based on the vdW radius is used instead of the iso-electron density surface determined by quantum chemical calculations. A group contribution method based on the universal functional group activity coefficient model (UNIFAC) is used to estimate the vdW surface area of repeating units in polymers. The predictions obtained by this simple parameter determination, named as the hybrid SLFV method, are compared with the experimental data for polyisobutylene and polystyrene solutions, and the predictivity of SLFV model is confirmed. The hybrid SLFV method demonstrates adequate predictivity for self-diffusion coefficients in polymer solutions for practical usability.