Takata Youichi, Hyono Atsushi, Ohshima Hiroyuki
Department of Chemical and Biological Engineering, National Institute of Technology, Ube College.
J Oleo Sci. 2016 Nov 1;65(11):903-908. doi: 10.5650/jos.ess16101. Epub 2016 Oct 12.
In order to elucidate an electroacoustic phenomenon of mixed micelles in an aqueous solution, we measured the colloid vibration current (CVI) in aqueous solutions of binary surfactant mixtures. Based on the thermodynamic treatment of critical micelle concentration (cmc) values determined by conductivity measurements, it was expected that dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) molecules would mix ideally in the micelle. However, the micelle composition as evaluated from the CVI measurement, based on the linear dependence of the CVI value on the micelle composition, differed from the aforementioned ideality. Considering these observations, we concluded that the CVI measurement was more sensitive to the counterion distribution near the micelle surface, whereas the thermodynamically determined micelle composition included the counterions more loosely bound in the diffuse double layer due to the electroneutrality condition included in its assumption. On the other hand, the phase diagram illustrating micelle formation in the lithium dodecyl sulfate (LiDS) - lithium perfluorooctane sulfonate (LiFOS) mixture system showed a heteroazeotropic point arising from the stronger interactions between homologous surfactants than between heterologous ones. Although the concentration dependence of CVI values was expected to drastically change at a heteroazeotropic point due to the enormous variation in the density of the micelle core, the results showed a monotonous change, which suggests that the density of the micelle core varies continuously. By taking the partial molar volume of fluorocarbon compounds in the hydrocarbon compounds into account, the density of the micelle core was affected by the size of the micelle as well as its constituents.
为了阐明水溶液中混合胶束的电声现象，我们测量了二元表面活性剂混合物水溶液中的胶体振动电流（CVI）。基于通过电导率测量确定的临界胶束浓度（cmc）值的热力学处理，预计十二烷基三甲基溴化铵（DTAB）和十二烷基三甲基氯化铵（DTAC）分子在胶束中会理想混合。然而，基于CVI值对胶束组成的线性依赖性，通过CVI测量评估的胶束组成与上述理想情况不同。考虑到这些观察结果，我们得出结论，CVI测量对胶束表面附近的抗衡离子分布更敏感，而热力学确定的胶束组成由于其假设中包含的电中性条件，包含了在扩散双层中结合较松散的抗衡离子。另一方面，说明十二烷基硫酸锂（LiDS）-全氟辛烷磺酸锂（LiFOS）混合体系中胶束形成的相图显示，由于同源表面活性剂之间的相互作用比异源表面活性剂之间的相互作用更强，出现了一个异共沸点。尽管由于胶束核心密度的巨大变化，预计在异共沸点处CVI值的浓度依赖性会急剧变化，但结果显示出单调变化，这表明胶束核心的密度是连续变化的。通过考虑碳氢化合物中碳氟化合物的偏摩尔体积，胶束核心的密度受到胶束大小及其成分的影响。
