Gemini surfactants are promising to replace conventional monomeric surfactants in various applications. In this paper, a new gemini surfactant with long unsaturated oleyl tails and bis(hydroxyethyl) ammonium head groups linked by butyl spacer was synthesized. Its critical micelle concentration in salt-free water (12 µM) is much lower than for its monomeric analog (220 µM). Without any additives this surfactant can form viscoelastic solutions with the viscosity of up to 1 kPa·s and elastic modulus of 15 Pa at the conditions, when the viscosity of the single-chained monomeric analog is close to that of pure water. These are one of the highest values reported so far for C18-tailed gemini surfactants without additives. The structure of the gemini surfactant solutions was studied by cryo-TEM and SAXS. Cryo-TEM revealed the presence of closed-looped micelles coexisting with linear wormlike micelles as well as the regular spacing between the micelles arising from strong electrostatic repulsion between them. The SAXS curves were well-fitted by a form-factor of core–shell cylinder, which yielded the radius of the core and the thickness of the shell equal to 1.4 nm each. Addition of n-decane induced the drop of viscosity by 6 orders of magnitude accompanied by the transformation of wormlike micelles into microemulsion droplets with 4.4 nm radius. Such gemini surfactants providing high viscoelasticity to aqueous solution that is responsive to added hydrocarbon are promising for the application in oil recovery as thickeners of fracturing fluids that can be cleaned up without any breakers at the backflow of oil.

中文翻译：

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水溶液中的新型长尾双子表面活性剂：自组装、流变特性和对碳氢化合物的响应性


Gemini 表面活性剂有望在各种应用中取代传统的单体表面活性剂。本文合成了一种新型双子表面活性剂，其具有长不饱和油基尾部和通过丁基间隔基连接的双(羟乙基)铵头基。其在无盐水中的临界胶束浓度 (12 µM) 远低于其单体类似物 (220 µM)。在不添加任何添加剂的情况下，当单链单体类似物的粘度接近纯水时，该表面活性剂可以形成粘度高达1 kPa·s、弹性模量为15 Pa的粘弹性溶液。这是迄今为止报道的不含添加剂的 C18 尾双子表面活性剂的最高值之​​一。通过冷冻 TEM 和 SAXS 研究了 Gemini 表面活性剂溶液的结构。冷冻透射电镜显示存在与线性蠕虫状胶束共存的闭环胶束，以及由于它们之间的强静电排斥而产生的胶束之间的规则间距。 SAXS 曲线与核壳圆柱体的形状因子非常吻合，核的半径和壳的厚度均等于 1.4 nm。正癸烷的添加导致粘度下降 6 个数量级，同时蠕虫状胶束转变为半径为 4.4 nm 的微乳液液滴。这种对水溶液提供高粘弹性且对添加的烃有响应的双子表面活性剂有望作为压裂液的增稠剂在采油中应用，并且可以在油回流时无需任何破胶剂进行清理。