Multiple-Stimuli-Responsive Surfactant-Free Microemulsions Based on Hydrophobic Deep Eutectic Solvents.

Hydrophobic deep eutectic solvents (HDESs) have been applied to colloidal systems such as microemulsions, despite the development of stimulus-responsive HDESs still being in a preliminary stage. Here, menthol and indole were hydrogen bonded to form CO2-responsiveness HDES. A surfactant-free microemulsion constituted of HDES (menthol-indole) as the hydrophobic phase, water as the hydrophilic phase, and ethanol as the double solvent was demonstrated to be CO2- and temperature-responsive. Dynamic light scattering (DLS) proved the single-phase region of the phase diagram, while conductivity and polarity probing techniques confirmed the kind of microemulsion. The ternary phase diagram and DLS methods were used to investigate the responsiveness of CO2 and effect temperature on the microemulsion drop size and behavior of the phase of the HDES/water/ethanol microemulsion. The findings revealed that when temperature increased, the homogeneous phase region increased. The droplet size in the homogeneous phase region of the associated microemulsion may be reversibly and accurately adjusted by adjusting the temperature. Surprisingly, a slight temperature change can cause a significant phase inversion. Furthermore, in the system, there was no demulsification in time for the CO2/N2 responsiveness process but rather the production of a homogeneous and pellucid aqueous solution.

CO2-Repurification Microemulsion Detergent for Oil-Based Slurry Cleaning.

In order to solve problems such as environmental pollution and pipeline blockage caused by oily wastewater after washing, N,N-dimethylcyclohexylamine (DMCHA) with CO2 response was selected as the oil phase, and an O/W microemulsion wellbore cleaning fluid with CO2 switching characteristics was successfully prepared with erucamide propyl betaine (EAB-40), sodium dodecyl benzene sulfonate (SDBS), n-butanol, silicone defoamer, and water. The water content of the microemulsion was 89.99%, and it had good stability at 40 and -5 °C. The emulsion was rapidly demulsified after being injected with CO2 in the CO2-repurification microemulsion detergent, and CO2 was removed with a N2 detergent. The emulsion was restored to its original state, which demonstrated the CO2/N2 switching properties of the emulsion. It is proven that the switching microemulsion has a good wetting transformation ability by cleaning the steel sheet and quartz sheet contaminated by oil-based slurry. The switching microemulsion system can clean the simulated wellbore contaminated by oil-based slurry, and the cleaning efficiency is above 99%. CO2 can be used at room temperature to separate oil and water from oily wastewater after cleaning.

CO2-Responsive Hydrophobic Deep Eutectic Solvent Based on Surfactant-Free Microemulsion-Mediated Synthesis of BaF2 Nanoparticles.

A new form of surfactant-free microemulsion (SFME) including hydrophobic deep eutectic solvent (HDES)/ethanol/water was constructed based on its CO2 response, and three regions, that is, HDES-in-water (HDES/W), bicontinuous (B.C.), and water-in-HDES (W/HDES) regions, were recognized. It is anticipated that SFMEs with tunable microstructures have outstanding applications as nanoreactors in reaction processes. The feasibility of preparing nanoparticles from HDES/ethanol/water SFME using barium fluoride (BaF2) as a model nanoparticle was investigated. HDES-based microemulsions benefit from HDES's excellent properties (novel, low toxicity, CO2-responsive, easy availability) and have potential in universal reactions, drug delivery, advanced material fabrication, etc. In this research, HDES-based microemulsions were prepared using HDES as the oil phase. Phase equilibria and microstructure were investigated using a ternary phase diagram, UV spectrophotometry, and the conductivity method. The CO2 switchable characteristics of the HDES-based microemulsions were investigated. HDES-based microemulsions were proposed as nanoreactors for the synthesis of barium fluoride nanomaterials. The microemulsion structure can modulate the size, morphology, and physicochemical properties of the nanoparticles through the CO2 switchable properties. It is argued that nanoreactors constructed with versatile HDES will offer a new direction for creation of cutting-edge scientific applications.