交联改性嵌段磺化芳香聚合物膜的微相分离结构调控和渗透汽化脱盐机理

Desalination by pervaporation offers unique advantages in handling brine and salinity wastewater. However, low water flux and a lack of understanding in its transport mechanism remain major obstacles to its application. Sulfonated aromatic block copolymer (SAP) consisting of an extremely hydrophobic backbone and an extremely hydrophilic region demonstrates self-assembly phenomena leading to a spontaneous microphase separation and the formation of nano-channels. This makes the polymer potential membrane materials with high water flux for desalination. Our research herein intends to prepare SAP membranes featured with strong hydrophilicity, high salt rejection and desirable physicochemical stability for pervaporation desalination. The high hydrophilicity of the membrane can be achieved from the ion-dipole interaction of the electriferous groups of polymer with water. The high salt rejection can be anticipated based on Donna effect between the charged groups and salt ions. The transport selectivity and stability will be improved by constructing ordered and rigid structure of hydrophobic backbone of the polymer. The mechanical strength and dimensional stability of the membrane will be enhanced by crosslinking, i.e. self-crosslinking and crosslinking with small molecules, linear polymers and hyperbranched polymers. A special focus will be paid on hyperbranched crosslinking to control and regulate the physicochemical properties, charge performance and microphase separation structure of the membrane. The correlation of micro structure, mesoscopic aggregation and macro morphology of the membrane with its physicochemical properties and separation performance will be investigated. Meanwhile, the interaction of water and salt ions with the active groups of the membrane will be explored. The research effort will be made on the construction of efficient water transport channel and the establishment of transport mechanism of the charged membranes for desalination by pervaporation. The pervaporation performance and long-term stability of the membrane will be assessed and the optimization of the membranes will be conducted. Finally, a complete system consisting of a novel approach, its theoretical fundamentals and technique supports to deal with brine and salty wastewater will be provided by this research.

渗透汽化脱盐在处理浓盐水和含盐废水方面具有独特优势，目前存在膜通量低、传递机理不明确的问题。磺化芳香聚合物材料内部可自发形成纳米传输通道，有望获得高的水通量。本申请拟开展嵌段磺化芳香聚合物膜的制备，利用材料固定电荷基团和水分子形成离子-偶极键合作用来提高膜的亲水性，利用电荷排斥效应达到高的盐截留率，利用其疏水骨架构筑规整刚性结构提高膜的选择性和物化稳定性。通过自交联、小分子交联、线性大分子交联、超支化聚合物交联等手段提高膜的机械强度和尺寸稳定性。重点开展超支化聚合物共混交联调控膜的物化性质、荷电性能和微相分离结构，研究其微观结构、介观聚集和宏观形貌与其物化性质和分离传输性能的关系，探究水和盐离子与膜材料活性基团的作用机制，构筑高效的水迁移通道，建立荷电膜渗透汽化脱盐的传递机理，评价和优化膜的渗透汽化性能，考察膜的长周期服役稳定性，为解决难处理浓盐水和含盐废水提供新途径、理论基础和技术支持。

渗透汽化脱盐在处理浓盐水和含盐有机废水方面具有独特优势，目前存在膜通量低、膜易于溶胀、脱盐传递机理不明确的问题。磺化芳香嵌段聚合物膜内部具有微相分离形成的亲水性纳米传输通道和荷电性能，为此，本研究采用该材料研制了具有应用潜力的新型渗透汽化脱盐膜材料。首先制备了高水通量的高磺化度聚苯乙烯-乙烯/丁烯-苯乙烯嵌段共聚物（S-SEBS）膜，通过热交联和乙二胺化学交联提高了膜的机械强度，采用小角散射和正电子湮灭表征手段分析了交联前后膜材料亲/疏水区域和自由体积的变化。然后，采用不同分子量的端羟基芳香族超支化聚酯和端氨基超支化聚醚酰胺，通过氢键交联、热交联、酸碱对交联，进一步提高了膜的机械强度，超支化分子结构的引入可拓展膜的亲水区间和增大自由体积，有利于保持良好的水传递速率。为进一步提高膜的综合性能，从分子链的化学结构设计入手，对S-SEBS接枝聚苯乙烯侧链，合成了新型的磺化芳香嵌段聚合物（S-SEBS-g-PSt）。由于侧链接枝引入额外苯环，提供了更多磺化位点，使该膜具有更高的磺酸根含量和亲水性。通过结构表征和动力学模拟，发现膜内亲水性区域尺寸和自由体积增大,水分子扩散系数增大，渗透汽化水通量和机械强度同时提升。均质膜（厚度20微米）在85℃下处理5wt%NaCl盐水的渗透汽化水通量达到50 kg/m2·h，盐截留率≥99.9%，达到国内外较好水平。在此基础上，还创新性地提出了基于苯环交联而不消耗磺酸根的新型交联策略，实现了交联膜兼具高通量、高截留率和良好机械强度的目标。该膜长期运行稳定，在处理高浓盐水和含盐废水方面具有应用前景和优势。利用分子动力学模拟从原子水平探究了膜的微相分离结构，明晰了渗透汽化脱盐过程的溶解扩散机理，剖析了空间位阻效应和荷电效应在盐离子扩散过程的协同作用，解释了膜本身具有高盐截留率的机制，为深入认识渗透汽化脱盐过程以及推动其实际应用提供了理论依据和基础数据。