Ionic Liquid-Based Microemulsions with Reversible Microstructures Regulated by CO₂

Abstract

CO2-responsive microemulsions based on ionic liquid 1,1,3,3-tetramethylguanidine-oleic acid (TMG-OA) have been designed to provide an approach for reducing the volatilization of amine in amine-containing microemulsions effectively and exhibit reversible transitions of microstructures. The ionic liquid TMG-OA was prepared by the direct neutralization of oleic acid (HOA) and 1,1,3,3-tetramethylguanidine (TMG, one of volatile and toxic amines). From the investigations of nuclear magnetic resonance hydrogen spectrum, pH, thermogravimetry, and automatic interface tension meter, the excellent properties of switchability, stability, and surface activity of TMG-OA were demonstrated, and then the ionic liquid-based microemulsions with CO2 response were prepared with TMG-OA (surfactant), HOA (oil phase), isopropyl alcohol (IPA, cosurfactant), and water. Interestingly, for microemulsions with a higher IPA content (47.42, 44.48 wt %), sizes of microemulsions are increased upon introducing CO2 and decreased upon addition of N2/65 °C. In addition, for microemulsions with a lower IPA content (26.22 wt %), the new microemulsions with different sizes are regenerated after the phase separation of emulsions generated by introducing CO2, and incomplete recovery of microemulsions can be observed upon addition of N2/65 °C. The reversible microstructures are induced by the swelling behavior and the reduced single phase area, which are caused by the reversible conversion between TMG-OA and HOA components.

pH-Responsive Regulation of a Surfactant-Free Microemulsion Based on Hydrophobic Deep Eutectic Solvents

“…Notably, the IPA content in HDES-based microemulsions was relatively high, which was conducive to the formation of microemulsions. 34 The ternary phase diagram (Figure 2B) is similar to that of the previously reported responsive SFMEs. 35,36 In general, an intuitive and effective method for analyzing the structure of microemulsions is conductivity measurement.…”

“…As shown in Figure 1D, these differences in decomposition temperatures could prove the success of HDES synthesis. 33,34 In addition, the physical properties of HDES were determined, as shown in Tabel S1. 6 Ternary Phase Diagram and Microstructures of Microemulsions.…”

Dual CO2 Responsiveness of an Oil-In-Water Emulsion by Using Sodium Oleate and Water-Soluble Tertiary Amines

“…As shown in the previous research, − the mixture of surfactants exhibits remarkable synergetic effect with a better performance than the single component, which might contribute to the demulsification of the system of water-soluble TA. As a traditional surfactant, sodium oleate (NaOA) can respond to CO 2 by itself.…”

Ionic Liquid‐Based Stimuli‐Responsive Functional Materials

“…The sizes of microemulsions are increased upon introducing CO 2 and decreased upon addition of N 2 . [ 60 ] As shown in Figure 3d, the selected samples (A), (B), and (C) exhibited the microstructures of oil‐in‐water (O/W) microemulsions, bicontinuous (BC) microstructure, and water‐in‐oil (W/O) microemulsions, respectively. The bicontinuous microstructure was formed with constant bubbling of CO 2 and recovered to the O/W microstructure after bubbling of N 2 at 65 °C for 90 min.…”