粘度法研究胶团的球-棒转变

本文基于粘度测量求得了溴化十四烷基吡啶胶团水溶液的特性粘度随盐量(0.5—2.0 mol L~(-1)NaBr), 温度(20°—40 ℃)和活性剂浓度(3-25 g L~(-1))的变化。利用Missel等提出的热力学模型,由此求算了支配球-棒转变的平衡常数K和多分散胶团的重均聚集数, 当盐浓度为0.5和1.0 mol L~(-1)时, 由粘度法在不同温度下得到的K值以及在30 ℃下随活性剂浓度的变化, 与光散射的相应结果相当一致。此外, 在不同温度下求得的参数K在一定的胶团浓度范围内保持为常量。这符合模型的要求。盐量增至2 mol L~(-1)时, K明显地具有浓度依赖性,并且两法给出的K和值都相差较大。上述模型不再适用。对于符合球-棒转变的胶团体系, 从特性粘度具有浓度依赖性出发的粘度方法是研究胶团长大的简单而可靠的方法, 能够提供很多重要的信息。

VISCOMETRIC STUDY OF SPHERE-TO-ROD TRANSITION OF AQUEOUS MICELLAR SOLUTIONS

Viscosity measurements of aqueous tetradecylpyridinium bromide solutions using a capillary viscometer have been made to determine the intrinsic viscosity of the micellar solutions as a function of salt concentration (0.5—2.0 mol L~(-1)NaBr), temperature (20—40 ℃), and amphiphile concentration (3—25 g/l). From the intrinsie viscosity values several basic micellar parameters including the thermodynamic parameter K, governing the sphere-to-rod transition in the micelle growth process, and the weight average aggregation number of polydisperse micelles, n_w, were calculated based on a thermodynamic model for micellization developed dy Missel et al. In both 0.5 and 1.0 mol L~(-1) NaBr solutions the parameter Kealuaed at various temperatures as well as the parameter n_w calculated as a function of amphiphile concentrtion at 30 ℃ are in good agreement with those obtained in our previous studies on TPB micellar properties by static and dynamic light scattering techniques. In addition, a constancy of K deduced from viscometric data over a suitable range of amphiphile concentrations, as required by the model, was observed at various temperatures. However, the parameter K becomes remarkably concentration-dependent and an obvious discrepancy in the determined parameters K and m_w between the two methods is observed under conditions of higher NaBr concentration (2 mol L~(-1)) which demostrates the invalidity of the model. It is therefore concluded that for amphiphile systems which display the sphere-to-rod transition behavior, the viscometric technique provides a simple, reliable approach to study micelle growth, extracting extensive information on amphiphile aggregation from a quantitative analysis of concentration-dependent intrinsic viscosities.