Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200, USA.
Langmuir. 2010 Jul 6;26(13):10532-40. doi: 10.1021/la100544w.
The effects of cosolvents (glycerol, ethanol, and isopropanol) on the self-assembly of novel alkyl-propoxy-ethoxylate surfactants in aqueous solutions have been investigated with a focus on the (i) quantification of solvent effects on the critical micelle concentration (cmc), (ii) free-energy contributions to micellization, (iii) local environment in the micellar solution, and (iv) structure of the micelles. The introduction of the polar organic solvents considered in this work into water decreases cohesive forces in the solvent mixture, resulting in an increase in the solubility of the surfactant molecules. As a result, micelle formation becomes less favorable and the cmc increases. The contribution of the cosolvent to the free energy of micellization is positive, and the data for different mixed solvents collapse onto a single straight line when plotted versus a function of the solubility parameters of the surfactant alkyl chains and the mixed solvents. The behavior of the poly(propylene oxide) part of the alkyl-propoxy-ethoxylate surfactants is hydrophilic, albeit less so in the ethanol-water mixed solvent than in plain water. Pyrene fluorescence emission I(1)/I(3) data suggest that the microenvironment in micellar solutions is affected mainly by the cosolvent concentration, not the surfactant degree of ethoxylation. Small-angle X-ray scattering data for both water and ethanol-water surfactant solutions are consistent with oblate ellipsoid micelles and reveal that the introduction of 20% ethanol decreases the micelle long axis by 10-15%.
共溶剂（甘油、乙醇和异丙醇）对新型烷氧基乙氧基醇表面活性剂在水溶液中自组装的影响进行了研究，重点关注：(i)溶剂对临界胶束浓度 (cmc) 的影响的定量，(ii)胶束化的自由能贡献，(iii)胶束溶液中的局部环境，和 (iv) 胶束的结构。在这项工作中考虑的极性有机溶剂引入水中会降低溶剂混合物中的内聚力，导致表面活性剂分子的溶解度增加。结果，胶束形成变得不太有利，cmc 增加。共溶剂对胶束化自由能的贡献是正的，并且当针对表面活性剂烷基链和混合溶剂的溶解度参数的函数绘制不同混合溶剂的数据时，它们会合并到一条直线上。烷氧基乙氧基醇表面活性剂的聚（环氧丙烷）部分的行为是亲水的，尽管在乙醇-水混合溶剂中不如在纯水中那么亲水。芘荧光发射 I(1)/I(3) 数据表明，胶束溶液中的微环境主要受共溶剂浓度影响，而不是表面活性剂的乙氧基化程度。水和乙醇-水表面活性剂溶液的小角 X 射线散射数据一致，呈扁长椭球胶束，并且表明引入 20%乙醇会使胶束长轴减少 10-15%。
