Ji Chunda, Zhou Chao, Zhao Bintao, Yang Jingfa, Zhao Jiang
Beijing National Research Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
Langmuir. 2021 May 11;37(18):5554-5562. doi: 10.1021/acs.langmuir.1c00309. Epub 2021 May 3.
The effect of binding strength of counterions with the polyelectrolyte chain to the swelling of polyelectrolyte brushes is studied, by investigating the swelling of both the polycation and polyanion in response to the variation of the salt concentration under the change of counterion's identity. Two polyelectrolyte brushes grafted on solid substrates are adopted: the cationic poly [2-(methacryloyloxy)ethyltrimethyl ammonium] (PMETA-X, X = F, Cl, Br, and I) and the anionic polystyrene sulfonate (M-PSS, M = Li, Na, K, and Cs). The swelling change with the salt concentration is investigated by ellipsometry, quartz crystal microbalance with dissipation, and dielectric spectroscopy. It is discovered that although the thickness of PMETA-X brushes is larger than that of M-PSS brushes of similar grafting density, the former has much less solvent incorporated than the latter. Such a difference is attributed to the weaker interaction between the PMETA chain and its halide counterions than that between the PSS chain and its alkali counterions, discovered by dielectric spectroscopy. This makes the original charges on the PMETA-X chain less neutralized and therefore have a higher charge density, compared with the M-PSS chain. The results demonstrate that the stronger binding of the counterions to the polyelectrolytes makes the main chains less charged, resulting in the weaker inter-chain electrostatic repulsion and less swelling of the brushes. Investigations into the effect of ion identity show the following order of binding strength: for the cationic PMETA chain, F < Cl < Br < I and for the anionic PSS chain, Li < Na < K < Cs.
通过研究在抗衡离子种类变化时，聚阳离子和聚阴离子在盐浓度变化下的溶胀情况，研究了抗衡离子与聚电解质链的结合强度对聚电解质刷溶胀的影响。采用了两种接枝在固体基质上的聚电解质刷：阳离子型聚[2-(甲基丙烯酰氧基)乙基三甲基铵](PMETA-X，X = F、Cl、Br和I)和阴离子型聚苯乙烯磺酸盐(M-PSS，M = Li、Na、K和Cs)。通过椭偏仪、带耗散的石英晶体微天平以及介电谱研究了盐浓度变化时的溶胀变化。发现尽管PMETA-X刷的厚度大于接枝密度相似的M-PSS刷，但前者所含的溶剂比后者少得多。这种差异归因于介电谱发现的PMETA链与其卤化物抗衡离子之间的相互作用比PSS链与其碱金属抗衡离子之间的相互作用弱。这使得PMETA-X链上的原始电荷中和程度较低，因此与M-PSS链相比具有更高的电荷密度。结果表明，抗衡离子与聚电解质的更强结合使得主链带电量减少，导致链间静电排斥减弱，刷的溶胀减小。对离子种类影响的研究表明结合强度顺序如下：对于阳离子型PMETA链，F < Cl < Br < I；对于阴离子型PSS链，Li < Na < K < Cs。
