Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China and The University of Chinese Academy of Sciences, Beijing 100049, China.
J Chem Phys. 2018 Oct 28;149(16):163329. doi: 10.1063/1.5035458.
Using sodium polystyrene sulfonate (NaPSS) and quarternized poly 4-vinylpyridine (QP4VP) as model systems, the chain conformation of polyelectrolytes under finite salt concentrations is investigated at a single molecular level. By fluorescence correlation spectroscopy (FCS), the hydrodynamic radius ( ) of the samples with the molecular weight ranging more than one order of magnitude was measured. The variations of as a function of molecular weight reveal the molecular weight dependence: under moderate salt concentrations (such as 10 and 0.1M), the shorter chains of both NaPSS and QP4VP take the rod-like conformation, while the longer chains take the coiled conformation (random coil or swelled random coil conformation, respectively). At high enough salt levels, both the charged chains take the coiled conformations. Photon counting histogram (PCH) measurements of the local pH value at the vicinity of the NaPSS chain expose the higher extent of counterion adsorption for longer chains as well as higher salt concentrations, telling that the charge regularization process is the major governing factor.
使用磺化聚苯乙烯钠 (NaPSS) 和季铵化聚 4-乙烯基吡啶 (QP4VP) 作为模型体系，在单分子水平上研究了有限盐浓度下聚电解质的链构象。通过荧光相关光谱 (FCS)，测量了分子量超过一个数量级的样品的流体力学半径 ( )。 作为分子量函数的 的变化揭示了分子量依赖性：在中等盐浓度（如 10 和 0.1M）下，NaPSS 和 QP4VP 的较短链呈现棒状构象，而较长链呈现卷曲构象（分别为无规线团或溶胀无规线团构象）。在足够高的盐水平下，带电荷的链都呈现卷曲构象。NaPSS 链附近局部 pH 值的光子计数直方图 (PCH) 测量揭示了较长链以及较高盐浓度下反离子吸附的更高程度，表明电荷规整化过程是主要的控制因素。
