Can Hatice, Kacar Gokhan, Atilgan Canan
Department of Chemistry, Science Faculty, Gebze Institute of Technology, P.O. Box 141, 41400 Gebze-Kocaeli, Turkey.
J Chem Phys. 2009 Sep 28;131(12):124701. doi: 10.1063/1.3236518.
We use dissipative particle dynamics simulations to explore the phase behavior and solution properties of ABCBA type model surfactants in near-supercritical CO(2) environment. We present design guidelines for functional surfactants with tunable properties. The block co-oligomers used in this study are made up of a CO(2)-phobic block having ethyl propionate and nine different types of ethylene monomers, flanked on either side by eight repeat units of fluorinated CO(2)-philic blocks. The most promising design block co-oligomer in the series is that with the longest CO(2)-phobic group in the ethylene monomers. For this particular oligomer, we systematically analyze the effect of concentration on the self-assembly behavior. Spherical micelles form in the 5%-65% volume fraction range for this oligomer, with the highest number of spherical micelles occurring at 45% surfactant in CO(2). When the volume fraction of the surfactant is increased from 70% to 85%, cylindrical micelles occur. We further investigate the effect of the length of the solvophilic fluorinated segments on self-assembly and find that stable micelles occur in a window of 8-14 repeat units. We find that the most critical contribution to stability is due to the mixing free energy between the chain tails residing in the outer layers and the interpenetrating molecules.
我们使用耗散粒子动力学模拟来探究ABCBA型模型表面活性剂在近超临界CO₂环境中的相行为和溶液性质。我们提出了具有可调性质的功能性表面活性剂的设计指南。本研究中使用的嵌段共聚物由一个具有丙酸乙酯和九种不同类型乙烯单体的CO₂疏水嵌段组成，两侧是八个重复单元的氟化CO₂亲水性嵌段。该系列中最有前景的设计嵌段共聚物是乙烯单体中具有最长CO₂疏水基团的那种。对于这种特定的共聚物，我们系统地分析了浓度对自组装行为的影响。对于这种共聚物，在5%-65%的体积分数范围内形成球形胶束，在CO₂中表面活性剂含量为45%时球形胶束数量最多。当表面活性剂的体积分数从70%增加到85%时，会出现圆柱形胶束。我们进一步研究了亲溶剂氟化链段长度对自组装的影响，发现稳定的胶束出现在8-14个重复单元的范围内。我们发现，对稳定性最关键的贡献来自于外层链尾与相互渗透分子之间的混合自由能。
