Department of Chemical Engineering and Materials Science, University of California, Davis, CA 95616, USA.
J Colloid Interface Sci. 2011 Apr 1;356(1):165-75. doi: 10.1016/j.jcis.2010.12.067. Epub 2010 Dec 28.
The gradient diffusion of ionic sodium dodecyl sulfate micelles in agarose gel was investigated at moderate concentrations above the CMC. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used to measure the gradient diffusion coefficient at three sodium chloride concentrations (0, 0.03, 0.10 M), three gel concentrations (0, 1, 2 wt%), and several surfactant concentrations. Time-resolved fluorescence quenching was used to measure aggregation numbers both in solution and gel. The micelle diffusivity increased linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle-micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The only exception was at 0.1M sodium chloride and 2 wt% agarose, which showed a slight reduction in the slope compared to 1 wt% agarose. It was found that the concentration effect is quite strong for charged solutes: at a NaCl concentration of 0.03 M in a 2% agarose gel, in a solution with 3% SDS micelles by volume, the micelle diffusion coefficient is doubled relative to its value in the same gel at infinite dilution. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement.
在高于 CMC 的中等浓度下，研究了离子十二烷基硫酸钠胶束在琼脂糖凝胶中的梯度扩散。特别感兴趣的是胶束、凝胶和氯化钠浓度对胶束扩散系数的影响。全息干涉法用于测量三个氯化钠浓度（0、0.03 和 0.10 M）、三个凝胶浓度（0、1 和 2 wt%）和几个表面活性剂浓度下的梯度扩散系数。时间分辨荧光猝灭法用于测量溶液和凝胶中的聚集数。在两个较大的氯化钠浓度和所有凝胶浓度下，胶束扩散系数随表面活性剂浓度呈线性增加。一般来说，这种效应的强度随氯化钠浓度的降低而增加，随凝胶浓度的增加而增加。这种行为表明，随着氯化钠浓度的增加，胶束-胶束静电相互作用减弱，随着凝胶浓度的增加，排除体积效应和流体力学屏蔽作用增强。唯一的例外是在 0.1M 氯化钠和 2wt%琼脂糖中，与 1wt%琼脂糖相比，斜率略有降低。结果表明，浓度效应对带电溶质相当强：在 2%琼脂糖凝胶中氯化钠浓度为 0.03 M 的情况下，在体积为 3%SDS 胶束的溶液中，胶束扩散系数相对于其在无限稀释相同凝胶中的值增加了一倍。与先前发表的理论预测相比，还比较了外推的无限稀释扩散系数和胶束扩散系数随表面活性剂浓度增加的速率，这些理论将胶束视为带电胶体球，将凝胶视为 Brinkman 介质。实验数据和理论预测吻合良好。
