College of Chemistry, Beijing Normal University, Beijing 100875, China.
Phys Chem Chem Phys. 2010 Jul 7;12(25):6732-41. doi: 10.1039/b924572c. Epub 2010 Apr 28.
Dielectric measurements were carried out on aqueous solution of poly(diallyldimethylammonium chloride) (PDADMAC) with different concentrations at room temperature. Additionally, for selected solutions the temperature dependence of dielectric relaxation spectroscopy (DRS) was examined in the range of 5-70 degrees C. The dielectric relaxation in the order of around MHz was observed, and the dielectric parameters were determined from the dielectric spectra by fitting data with the Cole-Cole equation. The dielectric parameters showed strong dependences on concentration and on temperature, respectively, and these dependences are analyzed by the scaling theory. From the analysis of concentration dependence of dielectric parameters, the dielectric relaxation is assigned to the localized fluctuation of uncondensed counter-ions over the distance between chains in dilute solution and correlation length in semi-dilute solution, respectively, and the solvent quality parameter for the uncharged polyelectrolyte chain is evaluated. By the analysis of temperature dependence of dielectric parameters, we find that: the physical meanings of the typical lengths of uncondensed counter-ions are not influenced by temperature; in semi-dilute solution, the highly extended length of the chain (correlation length) increases and the end-to-end distance of the chain decreases with increasing solution temperature; in the change process of dielectric relaxation of PDADMAC solution induced by the increase of temperature, the increment of ionic diffusion coefficient and decrement of permittivity of the solvent medium are the major factors. The enthalpy and entropy of activation of the dielectric relaxation are experimentally determined by the dependence of relaxation time on temperature, individually.
在室温下对不同浓度的聚二烯丙基二甲基氯化铵（PDADMAC）水溶液进行了介电测量。此外，对于选定的溶液，在 5-70°C 的温度范围内检查了介电弛豫光谱（DRS）的温度依赖性。观察到大约 MHz 数量级的介电弛豫，并且通过将数据拟合到 Cole-Cole 方程来确定介电谱中的介电参数。介电参数分别强烈依赖于浓度和温度，并且通过标度理论分析这些依赖性。从介电参数的浓度依赖性分析来看，介电弛豫分别分配给在稀溶液中链之间的距离和半浓溶液中的相关长度上的未凝聚抗衡离子的局部波动，并且评估了未带电聚电解质链的溶剂质量参数。通过分析介电参数的温度依赖性，我们发现：未凝聚抗衡离子的典型长度的物理含义不受温度影响；在半浓溶液中，链的高度扩展长度（相关长度）增加，并且随着溶液温度的升高，链的末端到末端距离减小；在 PDADMAC 溶液的介电弛豫过程由于温度升高而引起的变化中，离子扩散系数的增量和溶剂介质介电常数的减小是主要因素。通过依赖于弛豫时间的温度来单独确定介电弛豫的焓和熵的活化能。
