Jeong Kyeong-Jun, Yethiraj Arun
Theoretical Chemistry Institute and Department of Chemistry , University of Wisconsin , Madison , Wisconsin 53706 , United States.
J Phys Chem B. 2018 Apr 5;122(13):3259-3265. doi: 10.1021/acs.jpcb.7b08936. Epub 2017 Nov 21.
The self-assembly of surfactants into lyotropic liquid crystalline phases is interesting from a fundamental and practical perspective. The propensity for self-assembly is particularly interesting in Gemini surfactants which have a very low critical micelle concentration. In this work, we study the effect of headgroup identity on the driving force for the self-assembly of Gemini surfactants, using computer simulations of the potential of mean force (PMF). We find that surfactants with sulfonate headgroups have a greater tendency to assemble than those with carboxylate headgroups. The minimum in the PMF is about a factor of 2 deeper and occurs at shorter distances. Interestingly, the driving force is entropic with the carobxylate and energetic with the sulfonate headgroups. Analysis of different contributions suggests that these differences arise from surfactant headgroup electrostatics and size. The results provide an explanation for why the morphology diagram of the sulfonate surfactants is insensitive to temperature.
从基础和实际的角度来看，表面活性剂自组装成溶致液晶相是很有趣的。自组装倾向在临界胶束浓度非常低的 Gemini 表面活性剂中尤为有趣。在这项工作中，我们使用平均力势（PMF）的计算机模拟来研究头基特性对 Gemini 表面活性剂自组装驱动力的影响。我们发现，具有磺酸盐头基的表面活性剂比具有羧酸盐头基的表面活性剂具有更大的组装倾向。PMF 中的最小值大约深两倍，并且出现在更短的距离处。有趣的是，羧酸盐头基的驱动力是熵驱动的，而磺酸盐头基的驱动力是能量驱动的。对不同贡献的分析表明，这些差异源于表面活性剂头基的静电作用和尺寸。结果解释了为什么磺酸盐表面活性剂的形态图对温度不敏感。
