Estimation of solvent diffusion coefficient in amorphous polymers using the Sanchez–Lacombe equation-of-state

A modified free-volume model was proposed to predict the solvent diffusion coefficient in rubbery polymers without knowledge of any diffusion data. With the introduction of the Sanchez–Lacombe (SL) equation-of-state (EOS) into the Vrentas–Duda model, this model is an attempt to bridge the gap between the thermodynamic and transport properties of polymer solutions. The free volume provided by polymers for solvent diffusion can be estimated solely using the parameters of the SL EOS characteristics and the polymer glass transition temperature; thus the proposed model avoids the need to use polymer viscoelastic data in determination of polymer free-volume parameters. The other parameters in the Vrentas–Duda model remain applicable. Calculated results of solvent self- and mutual-diffusion coefficients of four common solvents in two polymers indicated that the modified model can give reliable predictions. In addition, it can reflect the effect of pressure on solvent diffusivity for concentrated polymer solutions.