School of Chemistry and Molecular Engineering, East China University of Science and Technology , Shanghai 200237, China.
Department of Chemistry, Lanzhou University , Lanzhou, Gansu 730000, China.
Langmuir. 2016 Dec 20;32(50):13464-13471. doi: 10.1021/acs.langmuir.6b03496. Epub 2016 Dec 12.
The liquid-liquid phase equilibria of [water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-decane] with the molar ratio w of water to AOT being 37.9 and [water/AOT/ethoxylated-2,5,8,11-tetramethyl-6-dodecyne-5,8-diol(Dynol-604)/n-decane] with w = 37.9 and the mole fraction α of Dynol-604 in the total surfactants being 0.158 were measured in this study. From the data collected in the critical region, the critical exponent β corresponding to the width of the coexistence curve was determined, which showed good agreement with the 3D-Ising value. A thermodynamic approach based on the Carnahan-Starling-van der Waals type equation was proposed to describe the coexistence curves and to deduce the interaction properties between droplets in the microemulsions. The interaction enthalpies were found to be positive for the studied systems, which evidenced that the entropy effect dominated the phase separations as the temperature increased. The addition of Dynol-604 into the (water/AOT/n-decane) microemulsion resulted in the decrease in the critical temperature and the interaction enthalpy. Combining the liquid-liquid equilibrium data for (water/AOT/n-decane) microemulsions with various w values determined previously, it was shown that the interaction enthalpy decreased with w and tended to change its sign at low w, which coincided with the results from the isothermal titration calorimetry investigation. All of these behaviors were interpreted by the effects of entropy and enthalpy and their competition, which resulted from the release of solvent molecules entrapped in the interface of microemulsion droplets and were dependent on the rigidity of the surfactant layers and the size of the droplet.
本研究测定了摩尔比 w 为 37.9 的[水/双（2-乙基己基）磺基琥珀酸钠（AOT）/正十二烷]和 w 为 37.9 的[水/AOT/乙氧基化-2,5,8,11-四甲基-6-十二炔-5,8-二醇（Dynol-604）/正十二烷]的液-液相平衡，其中 Dynol-604 在总表面活性剂中的摩尔分数α为 0.158。从临界区域收集的数据中，确定了对应共存曲线宽度的临界指数β，其与 3D-Ising 值吻合良好。提出了一种基于卡纳汉-斯塔林-范德华型方程的热力学方法来描述共存曲线，并推导出微乳液中液滴之间的相互作用特性。研究体系的相互作用焓为正值，这表明随着温度的升高，熵效应主导了相分离。向（水/AOT/正十二烷）微乳液中添加 Dynol-604 会降低临界温度和相互作用焓。将（水/AOT/正十二烷）微乳液的各种 w 值的液-液相平衡数据与之前确定的数据相结合，表明相互作用焓随 w 降低，并在低 w 值时趋于改变其符号，这与等温滴定量热法研究的结果一致。所有这些行为都可以通过熵和焓及其竞争的影响来解释，这是由于溶剂分子从微乳液液滴界面释放出来的结果，并且取决于表面活性剂层的刚性和液滴的大小。
