Polymer Research Institute, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu 610065, China.
Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China.
Molecules. 2023 Jun 7;28(12):4621. doi: 10.3390/molecules28124621.
pH-responsive viscoelastic fluids are often achieved by adding hydrotropes into surfactant solutions. However, the use of metal salts to prepare pH-responsive viscoelastic fluids has been less documented. Herein, a pH-responsive viscoelastic fluid was developed by blending an ultra-long-chain tertiary amine, -erucamidopropyl--dimethylamine (UCAMPM), with metal salts (i.e., AlCl, CrCl, and FeCl). The effects of the surfactant/metal salt mixing ratio and the type of metal ions on the viscoelasticity and phase behavior of fluids were systematically examined by appearance observation and rheometry. To elucidate the role of metal ions, the rheological properties between AlCl- and HCl-UCAMPM systems were compared. Results showed the above metal salt evoked the low-viscosity UCAMPM dispersions to form viscoelastic solutions. Similar to HCl, AlCl could also protonate the UCAMPM into a cationic surfactant, forming wormlike micelles (WLMs). Notably, much stronger viscoelastic behavior was evidenced in the UCAMPM-AlCl systems because the Al as metal chelators coordinated with WLMs, promoting the increment of viscosity. By tuning the pH, the macroscopic appearance of the UCAMPM-AlCl system switched between transparent solutions and milky dispersion, concomitant with a viscosity variation of one order of magnitude. Importantly, the UCAMPM-AlCl systems showed a constant viscosity of 40 mPa·s at 80 °C and 170 s for 120 min, indicative of good heat and shear resistances. The metal-containing viscoelastic fluids are expected to be good candidates for high-temperature reservoir hydraulic fracturing.
pH 响应型粘弹性流体通常通过向表面活性剂溶液中添加增溶剂来实现。然而，使用金属盐来制备 pH 响应型粘弹性流体的报道较少。本文通过将超长链叔胺 -erucamidopropyl--dimethylamine（UCAMPM）与金属盐（即 AlCl、CrCl 和 FeCl）混合，开发了一种 pH 响应型粘弹性流体。通过外观观察和流变学研究系统地考察了表面活性剂/金属盐混合比和金属离子类型对流体粘弹性和相行为的影响。为了阐明金属离子的作用，比较了 AlCl-和 HCl-UCAMPM 体系之间的流变性能。结果表明，上述金属盐使低粘度 UCAMPM 分散体形成粘弹性溶液。与 HCl 相似，AlCl 也可以将 UCAMPM 质子化为阳离子表面活性剂，形成蠕虫状胶束（WLMs）。值得注意的是，在 UCAMPM-AlCl 体系中表现出更强的粘弹性行为，因为 Al 作为金属螯合剂与 WLMs 配位，促进了粘度的增加。通过调节 pH 值，UCAMPM-AlCl 体系的宏观外观在透明溶液和乳白色分散体之间切换，同时粘度变化达一个数量级。重要的是，UCAMPM-AlCl 体系在 80°C 下具有 40 mPa·s 的恒定粘度，在 120 分钟内为 170 s，表明具有良好的耐热和耐剪切性能。含金属的粘弹性流体有望成为高温油藏水力压裂的良好候选材料。
