PVDF-PVP-DMAc-H2O铸膜液体系中浓相固化过程研究

研究了PVDF-PVP-DMAc-H2O体系的聚合物溶液固化的机理和速度.对PVDF聚合物凝胶进行了差示扫描量热实验和粉末衍射实验,表明聚合物溶液转变成凝胶固化是由结晶导致的物理可逆过程,结晶性液固分相按照成核-长大机理发生.通过落球实验测定了聚合物溶液体系从具有流动性的液态转换成凝胶态的过程,实验发现在凝胶点处从流动态转换成凝胶固态的过程大致需要2.5～4 min.光透射曲线法测定了成膜时的相分离速度, 结果表明成膜过程中,在凝胶分相后约1min出现了液液分相. 可见从开始发生液液分相到最后浓相固化、膜形态固定之间大致还有1.5～3 min的时间,这段时间是聚合物浓、稀相间的结构发生变化并最终固化定型的关键阶段.

The Polymer-rich Phase Solidification Process of PVDF-PVP-DMAc-H2O Solution

The solidification mechanism and rate of PVDF-PVP-DMAc-H2O membrane-casting solution were investigated. The differential scanning calorimeter (DSC) and the X-ray powder diffractometer (XRD) were used to analyze the properties of PVDF polymer gelation. It is found that the solidification process conversing from polymer solution to polymer gel is a physical-reversible process caused by crystallization, and the crystalline solid-liquid phase separation happens under the nucleation and growth mechanism. During the conversion process from polymer solution to polymer gel, the fluidity of the PVDF-PVP-DMAc-H2O system was detected by the falling-ball experiment. At the gelation point, the transformation process of fluid to solid takes about 2.5 to 4 minutes. The phase separation rate during the membrane formation process was measured by the light transmission method. The liquid-liquid phase separation happens at about 1 minute after the gel demixing. There is about 1.5~3 minutes left for the morphological variation between the polymer-rich and polymer-lean phase before the solidification of the polymer-rich phase, and it is the key period for the formatin, variation and finalization of the pores in the membrane.