Cao Zhonglin, Wu Sha, Zhang Guangzhao
Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, 230026, China.
Phys Chem Chem Phys. 2015 Jun 28;17(24):15896-902. doi: 10.1039/c5cp02111a. Epub 2015 May 28.
The dynamics of polyelectrolytes in salt-free solution is an unsolved problem. We have investigated the sedimentation and diffusion of xanthan and poly(N-methyl 4-vinyl pyridine iodide) (P4VPI) in salt-free dilute solutions by analytical ultracentrifugation (AUC) using sedimentation velocity (SV) as a function of polyelectrolyte concentration (Cp). Our study reveals two concentration regimes distinguished in either polyanion (xanthan) or polycation (P4VPI) dilute aqueous solution. When Cp is below the Debye concentration (Cd) at which the chain separation (d) is close to the debye length (lD), the interchain electrostatic repulsion is negligible, and the reciprocal apparent sedimentation coefficient (1/s), apparent diffusion coefficient (D) or reciprocal apparent molecular weight (1/Mw) is linearly related to Cp. In the range Cp > Cd with d < lD, the interchain electrostatic repulsion is present, and the dynamics of polyelectrolytes becomes complex. The real sedimentation coefficient (s0), the diffusion coefficient (D0) and the molecular weight (Mw,0) of the single polyelectrolyte chain in salt-free dilute solution can be obtained by extrapolating the concentration to zero. The present study reveals that the complex dynamics of polyelectrolytes in salt-free dilute solutions arises due to the interchain electrostatic repulsion.
无盐溶液中聚电解质的动力学是一个尚未解决的问题。我们通过分析超速离心法（AUC），以沉降速度（SV）作为聚电解质浓度（Cp）的函数，研究了黄原胶和聚（N-甲基4-乙烯基吡啶碘化物）（P4VPI）在无盐稀溶液中的沉降和扩散。我们的研究揭示了在聚阴离子（黄原胶）或聚阳离子（P4VPI）稀水溶液中区分出的两种浓度状态。当Cp低于德拜浓度（Cd）时，链间距（d）接近德拜长度（lD），链间静电排斥可忽略不计，表观沉降系数的倒数（1/s）、表观扩散系数（D）或表观分子量的倒数（1/Mw）与Cp呈线性关系。在Cp > Cd且d < lD的范围内，存在链间静电排斥，聚电解质的动力学变得复杂。通过将浓度外推至零，可以得到无盐稀溶液中单个聚电解质链的真实沉降系数（s0）、扩散系数（D0）和分子量（Mw,0）。本研究表明，无盐稀溶液中聚电解质的复杂动力学是由链间静电排斥引起的。
