亲水性两性离子聚合物刷的构象与结构

本文应用分子场理论,研究暴露于水蒸气中的亲水性两性离子聚合物(HP)刷的构象与结构.理论模型考虑HP-水(P-W)氢键和水-水(W-W)氢键效应,以及HP单体之间的偶极-偶极相互作用.研究发现,P-W与W-W氢键决定着HP的水合性,P-W氢键形成,会诱导HP刷溶胀.我们通过考察HP单体间的偶极-偶极相互作用发现,随着偶极-偶极相互作用增强,HP链在垂直培基表面沿着链方向,形成了结节状结构.这是由于HP单体之间的偶极-偶极静电吸引作用导致单体间汇聚结节,这种结节在刷内产生了较强的排斥体积作用,因此,这种HP刷具有抗污性能.在较高的接枝密度环境下,由于HP链间单体之间的偶极-偶极静电吸引作用,会形成链间单体-单体的结节,在刷内形成结节网络状凝胶结构,这种结构的出现,会使得HP刷呈现极强的抗污性.另外,当体系中水蒸气浓度增加、水合相互作用增强时,增加的P-W氢键将平衡HP单体之间的偶极-偶极相互作用,使得结节解开,聚合物链伸展.我们的理论结果符合实验观测,由此表明,P-W氢键效应,以及HP单体之间的偶极-偶极相互作用决定着HP刷的构象转变和结构特性,刷内出现的两性离子聚合物链内单体间的结节和链间单体结节状凝胶结构,是两性离子聚合物刷呈现较强抗污性的本质特性.

Structure and conformation of hydrophilic polyzwitterion brushes

Using a molecular theory, we investigate the structure and conformation of hydrophilic polyzwitterion brushes in water vapor. Our model takes polyzwitterion-water(P-W) hydrogen bonds, water-water(W-W) hydrogen bonds and dipole-dipole interactions between the segments. We found that P-W hydrogen bonds and W-W hydrogen bonds become key element in changing hydration of polyzwitterion brushes. P-W hydrogen bonds can induce switching of polyzwitterion brushes.We also investigated the dipole-dipole interactions between the polyzwitterion segments. It is clearly indicate the dipole-dipole interaction is key element in inducing presenting of knots between the segments inside the chain. Because of repulsive interactions between knots, antifouling properties of polyzwitterion brushes can be presented. At high grafting density, dipole-dipole interactions between the interchain segments lead to the network structure in polyzwitterion brushes, which is similar to gel. Thus the polyzwitterion brushes present the strong antifouling properties. On the other hand, hydration increases with increasing water vapor. Therefore, the P-W hydrogen bonds increase rapidly, which leads to an increasing repulsive interaction along polyzwitterion chains, which can balance the dipole-dipole interactions and make chain stretch. Our theoretical results agree well with the experimental observations. Our results indicate, because of P-W hydrogen bonds and dipole-dipole interactions between the segments, determined the structure and conformation of hydrophilic polyzwitterion brushes. The structures of knots in polyzwitterion brushes will take up less molecules, which lead to a antifouling properties of polyzwitterion brushes.