Prediction Of Thermodynamic Properties Of Solutions Based On COSMO-SAC Model And Lattice Model

In this study, the COSMO data of repeating units of commonly used polymers was obtained by quantum chemistry calculation. The COSMO data was then utilized to calculate the solubility parameter of polymers, and the Flory-Huggins parameter between polymers and solvents was achieved by various methods to calculate the phase diagram of ternary polymer solutions. Furthermore, the prediction for the properties of dope solutions was realized by fitting relative exchange energy parameters in Ising model with the COSMO-SAC model, which indicated significant guidance in the preparation of membranes.First, the COSMO data of repeating units for nine polymers was established by averaging the difference of the σ-profile of multimers according to Yang’s method. In addition, the effect of different methods for building the σ-profile of polymer, and the solution to deal with the negative value of distribution probability of the charge density was investigated. It is concluded that the pre-optimization of minimum repeating units could effectively reduce the time for geometry optimization without influencing the final results. Interestingly, when the distribution probability of the charge density was negative in the systemic average process, the replacement of real value by absolute value offered a superior result.Second, the COSMO-SAC model was introduced to calculate solubility parameter of polymers and the Flory-Huggins interaction parameter in absence of experimental data. The solubility parameter of polymers obtained by fitting the interaction parameter and solubility parameter of solvent exhibited an average deviation of 10.13%, which offered a theoretical guidance for the selection of solvent of dope solutions. Meanwhile, the average value of interaction parameter calculated by COSMO-SAC model and the interaction parameter calculated from the solubility parameter were both applied to calculate the phase diagram of ternary polymer solutions. It was suggested that the latter demonstrated a better result, which was further investigated in the applications of real systems.Finally, the COSMO-SAC model was expanded to ternary system to compare the distribution of excess Gibbs free energy with Ising model. Moreover, the exchange energy parameter in Ising model which directly obtained by surface fitting, was utilized to calculate the phase diagram of ternary solutions. Compared with the data in literature, it was found that the results varied in different systems, which indicated a necessary improvement for this method.