多价抗衡离子诱导聚甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEMA)刷构象转变的UCST行为

本文应用分子场理论,研究pH、Fe(CN)_6]~(3-)诱导聚甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEMA)刷的上临界溶解温度(UCST)构象转变与结构特性.理论模型考虑p H和Fe(CN)_6]~(3-)对PDMAEMA刷体系的静电调控作用.研究发现,在不同Fe(CN)_6]~(3-)浓度、不同p H条件下,PDMAEMA刷呈现了UCST构象转变行为.由于p H调节PDMAEMA单体质子化,Fe(CN)_6]~(3-)通过与PDMAEMA带正电荷的单体结合,形成了在PDMAEMA链内以Fe(CN)_6]~(3-)为中介的带电单体间的静电吸引结合.随着温度升高,Fe(CN)_6]~(3-)与PDMAEMA带正电荷的单体结合被破坏,Fe(CN)_6]~(3-)在链内凝聚导致的静电屏蔽效应减弱,PDMAEMA链内带电单体间的静电排斥增强,PDMAEMA刷的构象呈现了从塌缩到溶胀的UCST转变行为,并且在较高Fe(CN)_6]~(3-)浓度条件下,PDMAEMA刷构象转变的UCST增高.在较低p H值条件下,较多的PDMAEMA单体被质子化,Fe(CN)_6]~(3-)与PDMAEMA带正电单体的结合增强,PDMAEMA刷构象转变的UCST增大.基于pH和Fe(CN)_6]~(3-)对PDMAEMA刷体系中的静电调控效应,可以预言,在较小p H和较大Fe(CN)_6]~(3-)浓度条件下,PDMAEMA链在垂直培基表面沿着链方向形成结节状结构.这是由于以Fe(CN)_6]~(3-)为中介的链内带电单体间的静电吸引作用增强,导致临近单体间汇聚结节.我们的理论结果符合实验观测,由此表明,pH调节PDMAEMA单体的带电状态,以及Fe(CN)_6]~(3-)在PDMAEMA链内凝聚导致的静电屏蔽效应,决定着PDMAEMA刷的UCST构象转变和结构特性.

UCST behavior of polymethacrylate N,N-dimethylaminoethyl (PDMAEMA) brush switching induced by multivalent counterions

Using a molecular theory, we investigate that pH and Fe(CN)6]3− induce the upper critical solution temperature (UCST) switching and structure of N,N-dimethylaminoethyl methacrylate (PDMAEMA) brushes. The theoretical model considers the regulation of pH and Fe(CN)6]3−on the electrostatic interactions of the PDMAEMA brush. The results indicate that the PDMAEMA brush present switching of UCST at different Fe(CN)6]3− concentrations and different pH values. As the pH regulates the protonation of PDMAEMA segments, Fe(CN)6]3− can bind to positively charged segments of PDMAEMA, and the Fe(CN)6]3−-mediated attractive interaction along the chains can be presented. When the temperature rises, the binding of Fe(CN)6]3− to the positively charged segments of PDMAEMA is destroyed. Therefore, the screening of the electrostatic interactions caused by Fe(CN)6]3− condensing in the chain is weakened. The electrostatic repulsion between charged segments is enhanced. The PDMAEMA brush exhibits a UCST switching from collapse to swelling. At higher Fe(CN)6]3−concentration conditions, the UCST of the switching increases. At lower pH values, more PDMAEMA segments are protonated, and the binding of Fe(CN)6]3− to PDMAEMA positively charged segments is enhanced, which lead to UCST increase. Based on the effect of pH and Fe(CN)6]3−on the electrostatic regulation in the PDMAEMA brush, it can be predicted that Fe(CN)6]3− can induce presenting of knots between the segments inside the chain. This is because the electrostatic attraction interaction between charged segments in the chain mediated by Fe(CN)6]3−is enhanced, resulting in the convergence between adjacent segments. Our theoretical results are consistent with experimental observations, which indicate that the pH regulates the charged state of the PDMAEMA segments, and the electrostatic screening effect caused by Fe(CN)6]3−condensation in the PDMAEMA chain determines the UCST switching of the PDMAEMA brush and structure.