Microemulsions containing a responsive hydrophobic deep eutectic solvent (HDES) as the oil phase that can replace conventional organic solvents are considered to be a green strategy. It is anticipated that a pH-responsive HDES is synthesized to prepare rapid responsive surfactant-free microemulsions (SFMEs), which enable the transition from SFMEs to nanoemulsions. Menthol and n-octanoic acid (OA) were assembled into HDES by hydrogen bonding at a molar ratio of 1:2. The pH-responsive HDES as the oil phase and isopropyl alcohol (IPA) as the double solvent could form HDES/IPA/water SFMEs, which have unique responsiveness. Specifically, from the nuclear magnetic resonance hydrogen spectrum, pH, thermogravimetry, and Fourier transform infrared spectroscopy investigations, the excellent switchability and stability of menthol-OA were demonstrated. On the basis of these complexes, microemulsions were successfully prepared. Electrical conductivity and pH measurements were used to determine the structures of microemulsions and the phase inversion process. The effects of the contents of water and HDES, NaCl concentration, and pH of the system were investigated. Nanoemulsions were successfully prepared on the basis of the pH response of the microemulsions. In addition, the prepared nanoemulsion has a unique pH-responsive behavior that can be controllably regulated among nanoemulsions, microemulsions, and phase separation systems.

中文翻译：

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基于疏水性深共晶溶剂的无表面活性剂微乳液的 pH 响应调节

含有响应性疏水性深共熔溶剂（HDES）作为油相的微乳液可以替代传统的有机溶剂，被认为是一种绿色策略。预计合成一种 pH 响应型 HDES 可制备快速响应的无表面活性剂微乳液 (SFME)，从而实现从 SFME 向纳米乳液的转变。薄荷脑和n-辛酸 (OA) 通过氢键以 1:2 的摩尔比组装成 HDES。pH响应型HDES作为油相和异丙醇(IPA)作为双溶剂可以形成具有独特响应性的HDES/IPA/水SFMEs。具体而言，从核磁共振氢谱、pH、热重和傅里叶变换红外光谱研究中，证明了薄荷醇-OA 的优异可转换性和稳定性。在这些配合物的基础上，成功地制备了微乳液。电导率和 pH 值测量用于确定微乳液的结构和相转化过程。研究了水和 HDES 的含量、NaCl 浓度和系统 pH 值的影响。基于微乳液的pH响应成功地制备了纳米乳液。此外，制备的纳米乳液具有独特的pH响应行为，可以在纳米乳液、微乳液和相分离系统之间进行可控调节。