用状态方程改进的高聚物中溶剂扩散系数预测模型

将Simha-Somcynsky状态方程引入Vrentas-Duda自由体积理论模型,提出改进的高聚物-溶剂体系扩散系数模型,计算常压下橡胶态高聚物中有机溶剂扩散系数对浓度和温度的依存关系.利用高聚物结构单元的范德华体积导出高聚物自由体积分数表达式,通过Simha-Somcynsky方程求取高聚物体积以及对溶剂分子扩散有效的自由体积,避免原模型中繁琐的高聚物粘弹性实验测定和回归高聚物自由体积参数,提高了自由体积理论的预测能力.使用改进的模型预测了苯、甲苯、乙苯和三氯甲烷在聚苯乙烯、聚异丁烯和聚醋酸乙烯酯中的自扩散系数和互扩散系数,计算结果表明改进的自由体积模型具有较高的预测精度.

A Modified Predicted Diffusion Coefficient Model for Polymer-Solvent Systems Using an Equation-of-State

A modified free-volume model was proposed to calculate the solvent diffusion coefficients in polymers with introduction of the Simha-Somcynsky (SS) equation-of-state (EOS) into the Vrentas-Duda model. This model can predict concentration and temperature dependence of organic solvent diffusion coefficients in rubbery polymers under normal pressure. The expression of polymer fractional free volume was derived by the van der Waals volume of the polymer repeating units, and the volume of polymers as well as the free volume effective for solvent diffusion could be obtained by the SS EOS. The complicated process of measuring polymer viscoelasticity and regressing the polymer free-volume parameters in the Vrentas-Duda model could be avoided, therefore the prediction capability of the proposed model was improved. The modified model was employed to calculate solvent self-and mutual-diffusion coefficients of benzene, toluene, ethylbenzene and chloroform in polystyrene, polyisobutylene and poly(vinyl acetate), and the predictions are generally in good agreement with experimental results.