Capuzzi G, Baglioni P, Gambi C M, Sheu E Y
Department of Chemistry and CSGI, University of Florence, 50121 Florence, Italy.
Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 1999 Jul;60(1):792-8. doi: 10.1103/physreve.60.792.
The sodium counterion (Na+) of the sodium bis(2-ethylhexyl) sulfosuccinate (AOT) surfactant was exchanged with calcium Ca2+ to investigate the counterion charge effect on the structure of water in normal decane microemulsions. Ohmic conductivity and dielectric permittivity measurements were performed on samples at constant water to surfactant mole ratio [water]/[Ca(AOT)(2)]=26.6. Increasing the volume fraction of the dispersed phase phi, a percolation phenomenon was observed at the constant temperature of 25 degrees C. The percolation threshold was found at phi approximately 15% by Ohmic conductivity and static dielectric permittivity studied as a function of phi, and by the frequency dependence of the complex permittivity. Critical exponents typical of the static percolation mechanism (formation of bicontinuous microemulsions) were found below and above threshold. The comparison of these results obtained for the two different counterions, Ca2+ and Na+, in AOT surfactant water in normal decane microemulsions allows detection of an important difference. The percolation below threshold is dynamic for the sodium-based microemulsions, accounting for the formation of clusters of droplets, whereas calcium-based microemulsions show a static percolation. For this system, the coalescence of droplets begins to occur below threshold at phi approximately 12%.
将双（2-乙基己基）磺基琥珀酸钠（AOT）表面活性剂的钠离子反离子（Na+）与钙离子（Ca2+）进行交换，以研究反离子电荷对正癸烷微乳液中水结构的影响。在水与表面活性剂摩尔比[水]/[Ca（AOT）2]=26.6恒定的条件下，对样品进行了欧姆电导率和介电常数测量。在25℃恒温下，增加分散相φ的体积分数，观察到渗流现象。通过研究作为φ函数的欧姆电导率和静态介电常数，以及复介电常数的频率依赖性，发现渗流阈值在φ约为15%时出现。在阈值上下发现了典型的静态渗流机制（双连续微乳液的形成）的临界指数。对AOT表面活性剂在正癸烷微乳液中两种不同反离子Ca2+和Na+得到的这些结果进行比较，可以检测到一个重要差异。对于基于钠的微乳液，低于阈值的渗流是动态的，这解释了液滴簇的形成，而基于钙的微乳液则表现出静态渗流。对于该体系，在φ约为12%时，低于阈值时液滴开始聚并。
