Combining the Voigt creep model of viscoelastic solid and Flory - Huggins mixing model which are used to calculate the Gibbs free energy contributed by creep of polymer and mixing of polymer and penetrants

respectively

a transport model of penetrants in polymer membrane was established. The effect of model parameters on the sorption and desorption curves was simulated. The model can satisfactorily correlate the experimental sigmoid sorption curves and predict the corresponding desorption curves. It is shown that this model is more flexible and fewer model parameters are required as compared with Cranks model.