The current work investigates the effect of ethylene glycol (EG) on the surface and aggregation behavior of two ester-containing gemini surfactants (i.e., esterquat and betainate). EG, as a cosolvent, was added to aqueous surfactant solutions in three different percentages including 20, 35, and 50 (v/v %). The formation of surfactant aggregates was investigated using dynamic light scattering, zeta potential, and transmission electron microscopy. Several physical–chemical properties such as critical micelle concentration (cmc), Gibbs free energy of micellization (ΔG_mic^°), interfacial properties, degree of counterion dissociation (α), and morphology of aggregates were also determined in the absence and presence of EG. By increasing the concentration of EG in the surfactant solutions, the cmc and the minimum area per surfactant molecule (A_min) increased. Moreover, smaller aggregates were formed in the solutions with lower dielectric constant because of the increasing head–head repulsions. The ellipsoidal aggregates in water transformed into a spherical aggregate in the EG + water system. The zeta potential of the surfactant solutions decreased at higher EG concentrations, which was attributed to the formation of micelles with smaller hydrodynamic radii.

中文翻译：

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助溶剂对含酯双子表面活性剂聚集和胶束生长的影响

当前的工作研究了乙二醇（EG）对两种含酯双子表面活性剂（即酯季铵盐和甜菜碱）的表面和聚集行为的影响。将作为助溶剂的EG以三种不同的百分比（包括20、35和50（v / v％））添加到表面活性剂水溶液中。使用动态光散射，ζ电势和透射电子显微镜研究了表面活性剂聚集体的形成。几种物理化学性质，例如临界胶束浓度（cmc），胶束化的吉布斯自由能（ΔG _mic ^°），界面性质，抗衡离子解离度（α）和聚集体的形态也都在没有和存在EG的情况下确定。通过增加表面活性剂溶液中EG的浓度，cmc和每个表面活性剂分子的最小面积（A _min）都会增加。此外，由于头对头斥力的增加，在较小介电常数的溶液中形成了较小的聚集体。在EG +水系统中，水中的椭圆形聚集体转变为球形聚集体。在较高的EG浓度下，表面活性剂溶液的Zeta电位下降，这归因于形成了具有较小流体动力学半径的胶束。