A New Local CompositionModel for Phase Equilibrium Calculation of Binary Polymer Solutions

The new local composition model, Segmental-Wilson-NRF, based on the volume fraction is developed and a new excess Gibbs energy function for description of the binary polymer-solvent systems is obtained. This model for non-polymeric systems reduces to N-Wilson-NRF model. The activity coefficient of the new model consists of two parts, combinatorial and residual terms. In this work the S-Wilson-NRF are used for residual term and Flory-Huggins equations are applied for combinatorial term. The models with one temperature depended adjustable energy parameters are applied to correlate and predict the activity of solvent for 50 binary polymer solutions at various number-average molar mass of polymer and temperatures. In this work, the two different approaches are used for optimization of the solvent and segmental parameters. In the first approach, the two parameters are correlated for each binary polymer systems at the different conditions, however in the other approach we assume that the solvent and segmental interaction parameters are the same for the same binary polymer systems but they have the different numberaverage molar mass. Thus, using a temperature dependent relation for each parameter, only the two adjustable parameters for this group of systems are correlated. Using the first and second approaches, the overall root of mean square deviation (RMSD) are 0.018 and 0.037, respectively. The results show that the new model with the two different approaches is in good agreement with experimental data.