Hypothesis

Gemini surfactant 12–2–12 (dimethylene-1,2-bis(dodecyl dimethylammonium bromide)) solutions are known to show shear thickening and thinning under salt-free conditions. Because the rheological behavior of the wormlike micelles formed by 12–2–12 in solution is related to their structure, we expected that changes to the precursor structure would affect their rheological behaviors. It is also important to understand the effect of the introduction of a spacer group in the 12–2–12 molecules on the rheological behavior and structure of the wormlike micelles under shear flow.

Experiments

Simultaneous small-angle neutron scattering and rheological measurements (Rheo-SANS) of the 12–2–12 solutions were performed. We exhaustively studied the structural changes in the wormlike micelles upon increasing shear rate.

Findings

We found that the wormlike micelles were oriented in the direction of the flow due to elongation and that changes to the precursor of the wormlike micelles did not affect the shear thickening. As a precursor structural change of shear thinning, the wormlike micelles elongated while maintaining their orientation. We found that an increase in the molecular curvature of the 12–2–12 due to the introduction of a spacer-group contributed to the unusual rheological behaviors of the wormlike micelles in a solution under shear flow.

中文翻译：

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溶液中阳离子双子表面活性剂的胶束结构与流变行为关系的Rheo-SANS研究

假设

已知双子表面活性剂12–2–12（二亚甲基-1，2-双（十二烷基二甲基溴化铵）溶液在无盐条件下显示出剪切增稠和稀化的作用。由于溶液中12–2–12形成的蠕虫状胶束的流变行为与其结构有关，因此我们预期前体结构的变化会影响其流变行为。了解在剪切流作用下在12-2-12分子中引入间隔基对蠕虫状胶束的流变行为和结构的影响也很重要。

实验

同时进行了12–2–12解决方案的小角中子散射和流变学测量（Rheo-SANS）。我们详尽地研究了蠕虫状胶束在增加剪切速率时的结构变化。

发现

我们发现，由于伸长，蠕虫状胶束沿流动方向取向，并且蠕虫状胶束的前体的变化不会影响剪切增稠。作为剪切变薄的前体结构变化，蠕虫状胶束在保持其方向的同时伸长。我们发现，由于引入了间隔基团，使12–2–12的分子曲率增加，导致了剪切流下溶液中蠕虫状胶束的异常流变行为。