The key to surfactant-free microemulsion demulsification: CO2 promotes the transfer of amphiphilic solvent to aqueous phase

In recent years, research on surfactant-free microemulsion (SFME) has given us new insight into the field of microemulsion. Here, we report a SFME with CO2 responsiveness prepared by mixing 1-dodecanol (oil phase), aqueous phase and N,N-dimethylethanolamine (DMEA, amphiphilic solvent) at appropriate proportion. The proportion of the three components used to prepare SFME was obtained by analyzing the ternary phase diagram of DMEA, 1-dodecanol and water. Meanwhile, the microstructure transition characteristics of SFME from oil-in-water (O/W) to bicontinuous phase (B.C.) to water-in-oil (W/O) was characterized by electrical conductivity and UV-Vis spectroscopy. In addition, the CO2 response behavior of W/O microemulsion has been studied deeply. We found that a significant demulsification phenomenon when CO2 was introduced into this SFME system. By measuring the concentration of DMEA in 1-dodecanol after demulsification, the demulsification mechanism of SFME can be confirmed: The introduction of CO2 causes the protonation of DMEA, and this process makes the amphiphilic solvent more soluble in the aqueous phase, which results in destabilization of this ternary system. Eventually, with the continuous introduction of CO2, the separation of the oil and water phases of SFME occurs. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Recent research has provided new insights into the field of microemulsion through the study of surfactant-free microemulsion (SFME). In this study, a CO2-responsive SFME was prepared by mixing 1-dodecanol (oil phase), aqueous phase, and N,N-dimethylethanolamine (DMEA, amphiphilic solvent) at appropriate proportions. The microstructure transition characteristics of SFME were characterized, and the CO2 response behavior of water-in-oil (W/O) microemulsion was studied in depth. The demulsification mechanism of SFME was confirmed to be caused by the protonation of DMEA upon CO2 introduction, leading to the destabilization of the ternary system and eventual separation of the oil and water phases.