Electrochemical Control of Solution Viscoelasticity

研究了一种利用“法拉第（氧化还原）反应”控制流体粘弹性的新方法。该系统基于一种阳离子氧化还原可切换的二茂铁基表面活性剂[（11-二茂铁酰十一烷基）三甲基溴化铵，FTMA]，在水杨酸钠（鼻）存在下自组装成蠕虫状胶束。二茂铁基（还原形式）在分子中是疏水的，而铁离子（氧化形式）作为亲水的部分。这一性质使FTMA的亲水亲脂平衡发生了显著变化，从而改变了其聚集状态。FTMA（还原形式）和鼻腔的混合水溶液表现出显著的粘弹性。粘弹性行为符合麦克斯韦模型，零剪切粘度比水的粘度（1 × 10-3 Pass）高4个数量级（15 Pass）。在FF-TEM显微图上观察到相互纠缠的相当长的聚集体。因此，观察到的混合溶液的高粘弹性可以归因于蠕虫状胶束的纠缠网络。这种高粘弹性的水性混合物在+0.5 V vs. SCE下电解。经电氧化后，体系粘度急剧下降，弹性消失。氧化后的样品为牛顿流体，其粘度为2.5 × 10-3 Pass，约为还原后样品零剪切粘度的1/6000。这种显著的粘弹性下降是由于FTMA的亲水性增强，FTMA和鼻腔混合物的聚集状态从蠕虫状胶束到单体和/或其他更小的聚集体发生了显著变化。我们报告的方法适用于物质的控制释放，如被困在蠕虫状胶束纠缠网络中的染料和香水，喷墨打印机的墨水，使用电信号的流量控制系统，变速箱和阀门的离合器。

A novel way of controlling fluid viscoelasticity using a "Faradaic (redox) reaction was studied. The system is based on a cationic redox-switchable ferrocenyl surfactant [(11-ferrocenylundecyl) trimethylammonium bromide, FTMA] that self-assembles into worm-like micelles in the presence of sodium salicylate (NaSal). The ferrocenyl group (reduced form) in the molecule is hydrophobic, while the ferricinium cation (oxidized form) acts as a hydrophilic moiety. This property gives remarkable change in the hydrophilic-lipophilic balance of FTMA, thereby changing its aggregation state.An aqueous solution of mixed FTMA(reduced form) and NaSal exhibited a remarkable viscoelasticity. The viscoelastic behavior corresponded to a Maxwell-model and the zero shear viscosity was four orders of magnitude (15 Pass) higher that the viscosity of water (1x 10-3 Pass). Considerably elongated aggregates that are entangled with each other were observed on the FF-TEM micrograph. The high viscoelasticity observed for the mixed solution can therefore be ascribed to an entangled network of worm-like micelles.This highly viscoelastic aqueous mixture was electrolyzed at +0.5 V vs. SCE. The viscosity of the system dramatically decreased and the elasticity disappeared after electric oxidation. The oxidized sample was a Newtoniam fluid and its viscosity had a value of 2.5x 10-3 Pass, which is about 1/6000 of the zero shear viscosity of the reduced sample. This remarkable viscoelasticity decrease is caused by a significant change in the aggregation state of FTMA and NaSal mixture from worm-like micelles to monomers and/or other smaller aggregates due to the enhanced hydrophilicity of FTMA. The method that we report are applicable to the controlled release of substances such as dyes and perfumes entrapped in an entangled network of worm-like micelles, ink for inkjet printers, flow rate controlling systems using electrical signals, clutches for transmission and valves.