超(亚)临界R134a中聚苯乙烯发泡行为的平衡与非平衡性质研究

The new foamer supercritical (subcritical) 1,1,1,2-tetrafluoroethane (R134a) has more dissolvable quality for polymer, lower flow resistance and higher diffusion coefficient compared with supercritical carbon dioxide, and it maybe improve the widely low rate of hole connection and low efficiency of heterogeneous nucleation for polymer foaming. Both experimental and theoretical research will be done systematically to acquire the knowledge of equilibrium and non-equilibrium property of the asymmetric system of supercritical (subcritical) R134a and polystyrene, such as the dissolution equilibrium and surface properties, the heterogeneous nucleation and growth. According to the modern statistical mechanics theory, the foaming mechanism will be revealed from the molecular level. Firstly,three-dimentional integral equation would be applied, as well as, the bridge function will be introduced to correct the asymmetrical property of the supercritical (subcritical) R134a and polystyrene system, and then the dissolution equilibrium model for the above system will be proposed. Secondly,in order to get the surface tension model, density functional theory will be connstructed and each free energy functional expression will be proved to accommodate the system investigated. Thirdly,the three-dimentional dynamic density functional theory will be adopted to deal with the heterogeneous bubble nucleation and growth process, together with research on the effect of viscous force that could restrict the growth of the nucleus. At the same time, experimental research will be performed to determine the dissolution equilibrium, surface tension, viscosity of the supercritical (subcritical) R134a and polystyrene system, which could verify the new proposed models and provide technical support for the development and application of the supercritical (subcritical) R134a foaming polymer process.In this work, the molecular force field parameters of supercriticla (subcritical) R134a and polystyrene were all taken from the universal force field,therefore,the properties of binary and multiple systems will be predicted , and it does not need to introduce any empirical parameters, which makes the proposed mathematical model in this work has rigorous theoretical foundation and will be widely used in other polymer foaming process.

与超临界CO2比，新型发泡剂超(亚)临界R134a与聚合物互溶性好，在聚合物中流动阻力小、扩散系数大，可改善目前普遍存在的气体发泡孔洞连接率低和非均相成核效率低问题。本文率先对超(亚)临界R134a/聚苯乙烯非对称体系平衡性质(如溶解平衡、表面性质)和非平衡性质(如非均相成核与长大)展开研究。依据现代统计力学理论，从分子层面揭示发泡机理。应用三维聚合物积分方程，引入桥函数校正R134a/聚苯乙烯体系的非对称性，推导溶解平衡模型；应用密度泛函模型研究体系的表面张力，通过构建模型中各项自由能泛函的表达式，得到表面张力计算模型；应用三维动力学密度泛函理论研究体系的非均相气泡成核及生长过程，考察粘滞力对气泡长大的延迟效应。同时，实验测定体系的溶解平衡、表面张力和粘度等，为验证模型和工艺开发提供支持。本文所有分子力场参数均取自于通用力场，所建模型均有严格的理论基础，无需任何经验参数，具有广泛适用性。

针对聚合物发泡工艺中气体发泡孔洞连接率低和聚合物非均相成核效率低的问题，本课题按照项目计划书，应用现代统计力学理论，从微观分子层面研究了超（亚）临界R134a/聚苯乙烯高度非对称体系的平衡性质（如相平衡、界面性质）和非平衡性质（如非均相成核与长大），为超（亚）临界流体发泡聚合物工艺提供理论依据。首先，应用三维聚合物积分方程理论和统计缔合流体理论，通过引入桥函数对R134a/聚苯乙烯体系的高度非对称性进行了校正，建立了聚合物和超（亚）临界流体体系的相平衡模型，验证了模型的可靠性，计算了聚苯乙烯每个单体周围R134a分子的三维空间分布，得到了溶质聚合物和三亚苯在超（亚）临界R134a流体中的溶解度。其次，应用密度泛函理论，改进了模型中相应自由能泛函的表达式，计算了R134a在聚苯乙烯中的溶解度、聚苯乙烯的膨胀系数、R134a/聚苯乙烯体系的界面密度分布和界面张力。然后，采用充分检验过的密度泛函理论模型，考虑R134a在流动过程中产生的粘滞力对气泡长大的延迟效应，建立动力学密度泛函理论模型，计算R134a气泡在聚苯乙烯表面非均相成核的临界半径及成核自由能等参数，阐明了超（亚）临界流体R134a发泡聚苯乙烯过程中非均相气泡成核及生长等非平衡问题。实验研究方面：采用静态法测定了聚苯乙烯、聚乙烯吡咯烷酮、聚丙烯酰胺、聚乙烯醇、邻硝基苯甲酸、邻氨基苯甲酰胺、芦丁、三亚苯、肉桂酸、十二烷基硫酸钠和D-柠檬烯，共十一种固体溶质在亚临界R134a流体中的溶解度，并得到了超（亚）临界R134a/聚苯乙烯体系、界面张力和粘度等基础数据；另外，为了对比上述溶质在亚临界R134a和超临界CO2流体中的溶解度，本课题采用动态法测定了上述溶质在超临界CO2流体中的溶解度。这些基础数据和理论研究结果可为高性能聚合物发泡材料的制备工艺提供理论指导和技术支持。