咪唑类离子液体中聚(N-异丙基丙烯酰胺)凝胶的体积相变行为

Volume Phase Transition Behavior of Poly(N-isopropylacrylamide)Gels in Imidazolium-Based Ionic Liquids

通过热引发的方法制备了聚(N-异丙基丙烯酰胺)(PNIPAM)水凝胶,对PNIPAM水凝胶进行真空冷冻干燥与溶剂置换后得到PNIPAM离子液体凝胶。通过扫描电镜(SEM)及温敏平衡体积溶胀实验分别表征了PNIPAM凝胶的微观结构和PNIPAM凝胶在真空干燥前后的离子液体中体积相变行为。SEM结果表明,真空冷冻干燥后的PNIPAM凝胶具有大量微米级网络结构;温敏平衡体积溶胀实验表明,相同温度下PNIPAM离子液体凝胶的平衡体积随着离子液体阳离子上取代烷基的增长而增大,与真空干燥后的离子液体中的体积相变行为相比,在未真空干燥的离子液体中,PNIPAM离子液体凝胶在低温下的平衡体积显著减小、体积溶胀比增大。说明阳离子取代烷基链的增长有利于PNIPAM在离子液体中的溶胀,且水分对其体积相变行为有较大影响。

Poly(N-isopropylacrylamide)(PNIPAM)hydrogels were prepared by thermal initiation polymerization.The PNIPAM ionic liquid gels were formed by vacuum freeze-drying and solvent replacement.The microstructures and volume phase transition behaviors of PNIPAM gels in ionic liquids before and after vacuum drying were characterized by SEM and temperature-sensitive swelling experiments,respectively.SEM results show that the vacuum freeze-dried PNIPAM gels have a large number of micron-scale network structures.Temperature-sensitive swelling experiments show that the equilibrium volume of PNIPAM ionic liquid gels increases with the increase in length of substituted alkyl groups on ionic liquid cations at the same temperature.The equilibrium volume of PNIPAM ionic liquid gels decreases significantly at low temperature and the volume swelling ratio increases in undried ionic liquids compared with vacuum dried ionic liquids.The results indicate that the increase in length of cation-substituted alkyl chains is favorable to the swelling of PNIPAM gels in ionic liquids,and moisture has a great effect on volume phase transition behavior.