Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China , Hefei, P. R. China 230026.
Langmuir. 2017 Jul 11;33(27):6838-6845. doi: 10.1021/acs.langmuir.7b01395. Epub 2017 Jun 29.
Strong polyelectrolyte brushes (SPB) and weak polyelectrolyte brushes (WPB) have different origins with response to pH, which makes their pH-responsive properties sensitive to salt concentration in different ways. Herein, we have employed poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC) and poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes as model systems for SPB and WPB, respectively, to investigate the effect of salt concentration on the pH responses of SPB and WPB using several surface-sensitive techniques. The pH-responsive properties of the PMETAC brushes are governed by the reorganization of the interchain hydrogen bonds between the grafted chains, whereas the pH response of the PDMAEMA brushes is controlled by the charge of the grafted chains. The response of the properties of the PMETAC brushes including hydration, conformation, and surface wettability becomes weaker with increasing salt concentration induced by the competitive adsorption of counterions to the brushes between OH and Cl. The weakening of the pH response of the PMETAC brushes is more remarkable at the relatively high pH values. The pH response of the PDMAEMA brushes also exhibits a salt-concentration dependence. As the salt concentration increases, the weakening of the pH response of the PDMAEMA brushes is attributed to the decrease in osmotic pressure within the brushes at relatively low pH values.
强聚电解质刷（SPB）和弱聚电解质刷（WPB）具有不同的起源和对 pH 的响应，这使得它们的 pH 响应特性对盐浓度的敏感方式也不同。在此，我们分别采用聚[2-（甲基丙烯酰氧）乙基三甲基氯化铵]（PMETAC）和聚[2-（二甲氨基）乙基甲基丙烯酸酯]（PDMAEMA）刷作为 SPB 和 WPB 的模型体系，使用几种表面敏感技术研究了盐浓度对 SPB 和 WPB pH 响应的影响。PMETAC 刷的 pH 响应特性受接枝链间氢键的重组控制，而 PDMAEMA 刷的 pH 响应受接枝链电荷控制。PMETAC 刷的性质响应，包括水合作用、构象和表面润湿性，随着盐浓度的增加而减弱，这是由于抗衡离子在 OH 和 Cl 之间与刷之间的竞争吸附引起的。PMETAC 刷的 pH 响应在相对较高的 pH 值下减弱更为明显。PDMAEMA 刷的 pH 响应也表现出盐浓度依赖性。随着盐浓度的增加，PDMAEMA 刷的 pH 响应减弱归因于相对低 pH 值下刷内渗透压的降低。
