聚酰胺复合纳滤膜的分离性能主要由聚酰胺分离层决定。在界面聚合反应过程中,有机相溶剂的物理性质影响两相单体在界面的溶解及扩散行为,使聚酰胺分离层微观形貌结构发生变化,从而改变膜性能。以异构烷烃混合型溶剂Isopar G、Isopar H、Isopar L、Isopar M为有机相溶剂采用界面聚合法制备聚酰胺复合纳滤膜,考察上述有机相溶剂对复合纳滤膜聚酰胺交联度、分离层微观结构、聚酰胺高分子链堆积程度的影响,通过分析有机相溶剂物理性质与纳滤膜分离性能、聚酰胺层结构参数之间的相关性,探究有机相溶剂对纳滤膜分离性能的影响机制。结果表明,有机相溶剂的表面张力与聚酰胺高分子团簇的分形维数Dm呈强相关性,相关性系数为-0.98；分形维数Dm与复合纳滤膜的水透过系数A呈强相关性,相关性系数为0.95,即通过选取表面张力较低的有机相溶剂,有利于提高聚酰胺高分子的分形维数,使聚酰胺具有更高的链密度,短分子链结构堆积更加疏松,从而制备具有更高水通量的聚酰胺复合纳滤膜。有机相溶剂的表面张力与水透过系数A的相关性系数为-0.97,进一步印证上述结论。
The performance of polyamide (PA) thin film composite (TFC) nanofiltration (NF) membrane is mainly determined by the polyamide thin layer. Physical properties of organic solvents in the interfacial polymerization (IP) process affect the diffusion and dissolution behavior of monomers in aqueous and organic phase at their interface, thus influence the microstructure of PA layer and the separation performance of NF membranes. Here, TFC NF membranes with PA layers were prepared via IP process by different iso-alkane solvents, including Isopar G, Isopar H, Isopar L and Isopar M as the organic phase solvents, and the crosslinking degree of PA polymer, microstructure of PA layer and the stacking degree of the PA clusters were systematically investigated based on these NF membranes. The correlation coefficient between physical properties of these organic solvents and the structural parameters of PA layer, together with the performance of NF membrane were explored. Results revealed that the surface tension of organic solvents had strong correlation with the fractal dimension (Dm) of PA polymer, showing the correlation coefficient of -0.98. Meanwhile, the fractal dimension had strong correlation with the water permeability coefficient (A), possessing the correlation coefficient of 0.95. It indicated that, fractal dimension of PA polymer increased by choosing organic solvent with low surface tension, thus improving the water flux of NF membranes due to the higher PA chain density and looser stacking of PA clusters. The correlation coefficient between the surface tension of organic solvent and A was -0.97, which further confirmed this conclusion.