Chu Xiao, Yang Jingfa, Liu Guangming, Zhao Jiang
Beijing National Laboratory for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Soft Matter. 2014 Aug 14;10(30):5568-78. doi: 10.1039/c4sm00860j.
It has been observed previously that when permanently charged polyelectrolyte brushes are exposed to an external salt solution, they shrink when the salt level is high enough. In this study, we observed an enhanced swelling process before the salt concentration reached that limit. We systematically investigated a few strong polyelectrolyte brush systems, including sodium polystyrene sulfonate (PSSNa), poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (PMETAC) and potassium poly(3-sulfopropyl methacrylate) (PSPMA) with different molecular weights and grafting density using a combination of methods, including ellipsometry, quartz crystal microbalance with dissipation (QCM-D) and atomic force microscope (AFM). The swelling enhancement is expressed by the thickening of the brush layer at moderate salt concentrations, accompanied by the decrease of refractive index, the increase of the amount of solvent inside the brushes and an increase in retardation time. A scenario is proposed in which the counterions penetrate into the brushes driven by the external salt ions, they disrupt and break up the previously formed multiplets due to the dipole-dipole interaction by the ion-pairs on the polymer chain. This process results in the release of the bound segments and the stretching of the polymer chains.
此前已经观察到，当永久带电的聚电解质刷暴露于外部盐溶液中时，当盐浓度足够高时它们会收缩。在本研究中，我们观察到在盐浓度达到该极限之前有一个增强的溶胀过程。我们使用多种方法，包括椭偏仪、带耗散的石英晶体微天平（QCM-D）和原子力显微镜（AFM），系统地研究了几种强聚电解质刷体系，包括不同分子量和接枝密度的聚苯乙烯磺酸钠（PSSNa）、聚（[2-（甲基丙烯酰氧基）乙基]三甲基氯化铵）（PMETAC）和聚（3-磺丙基甲基丙烯酸酯）钾（PSPMA）。溶胀增强表现为在中等盐浓度下刷层增厚，同时伴随着折射率降低、刷内部溶剂量增加以及延迟时间增加。提出了一种情况，即抗衡离子在外加盐离子的驱动下渗透到刷中，它们由于聚合物链上离子对的偶极-偶极相互作用而破坏并分解先前形成的多重态。这个过程导致结合链段的释放和聚合物链的伸展。
