Departamento de Física, Universidade Federal de Santa Catarina, Florianópolis, Santa Catarina 88040-900, Brazil.
J Chem Phys. 2010 Feb 14;132(6):064905. doi: 10.1063/1.3316133.
A lattice model for amphiphilic aggregation in the presence of a structured waterlike solvent is studied through Monte Carlo simulations. We investigate the interplay between the micelle formation and the solvent phase transition in two different regions of temperature-density phase diagram of pure water. A second order phase transition between the gaseous (G) and high density liquid (HDL) phases that occurs at very high temperatures, and a first order phase transition between the low density liquid (LDL) and (HDL) phases that takes place at lower temperatures. In both cases, we find the aggregate size distribution curve and the critical micellar concentration as a function of the solvent density across the transitions. We show that micelle formation drives the LDL-HDL first order phase transition to lower solvent densities, while the transition G-HDL is driven to higher densities, which can be explained by the markedly different degrees of micellization in both cases. The diffusion coefficient of surfactants was also calculated in the LDL and HDL phases, changing abruptly its behavior due to the restructuring of waterlike solvent when we cross the first order LDL-HDL phase transition. To understand such behavior, we calculate the solvent density and the number of hydrogen bonds per water molecule close to micelles. The curves of the interfacial solvent density and the number of hydrogen bonds per water molecule in the first hydration signal a local phase change of the interfacial water, clarifying the diffusion mechanism of free surfactants in the solvent.
通过蒙特卡罗模拟研究了存在结构化类水溶剂时两亲物聚集的格子模型。我们研究了在纯水的温度-密度相图的两个不同区域中胶束形成与溶剂相转变之间的相互作用。在非常高的温度下发生气态（G）和高密度液体（HDL）相之间的二级相变，以及在较低温度下发生低密度液体（LDL）和（HDL）相之间的一级相变。在这两种情况下，我们都发现了在相变过程中作为溶剂密度函数的聚集大小分布曲线和临界胶束浓度。我们表明，胶束形成将 LDL-HDL 一级相转变驱动到较低的溶剂密度，而 G-HDL 转变则驱动到较高的密度，这可以通过两种情况下明显不同的胶束化程度来解释。还在 LDL 和 HDL 相中计算了表面活性剂的扩散系数，由于我们穿过 LDL-HDL 一级相转变时类水溶剂的重新结构，其行为突然发生变化。为了理解这种行为，我们计算了靠近胶束的溶剂密度和每个水分子的氢键数。第一水合层中界面溶剂密度和每个水分子氢键数的曲线表明界面水的局部相变化，阐明了溶剂中游离表面活性剂的扩散机制。
