水蒸气诱导两性离子聚合物刷的构象转变

我们把Flory Huggins模型(association models)推广应用到暴露于水蒸气中的两性离子聚合物刷体系,考虑两性离子聚合物-水氢键(P-W氢键)与两性离子聚合物链间两亲离子单体-单体键合(zwitterions complex)、形成氢键与两性离子聚合物链构象的耦合特性,研究水蒸气诱导的两性离子聚合物刷构象转变的机理和相行为.研究发现,随着水蒸气浓度的增加,P-W氢键效应会使得两性离子聚合物刷溶胀;两亲离子单体-单体键合效应会导致水分子将会被排出刷外,并会导致两性离子聚合物刷塌缩.通过分析两性离子聚合物刷的相图发现,P-W氢键效应在决定两性离子聚合物刷的相行为中起到主导作用,在水蒸气增加过程中两性离子聚合物刷将会单调溶胀.基于本文的分析,可以预言,由于P-W氢键效应,两性离子聚合物刷可以吸附水蒸气,当两性离子聚合物链接枝密度足够高时,两性离子聚合物刷内的水分子将会被排出,并会形成两亲离子单体-单体键合连接的凝胶状结构.

Switching of polyzwitterion brushes by water vapor

We presented a theory to study switching of polyzwitterion brushes by water vapor. Our theory model takes account of polyzwitterion-water(P-W) hydrogen bonds and zwitterions complex. We found that P-W hydrogen bonds become a key element in inducing swelling of polyzwitterion brushes. Our results indicate, because of zwitterionic complexes, the polyzwitterionic brushes take up less water molecules, which lead to a decline in water volume fraction in polyzwitterion brushes. We also investigated the phase diagram of polyzwitterion brushes. It is clearly indicate P-W hydrogen bonds are key elements in inducing swelling of polyzwitterion brushes, and water vapor induce polyzwitterion brushes swell monotonically.On basis of our theory approach, we can predict that, because of P-W of hydrogen bonds, polyzwitterion brushes can adsorb water vapor; When the grafting density is too large, zwitterionic hybridization will lead to a zwitterionic complexe network formation of 3D polyzwitterion brushes.