CO2-Responsive Surfactant-Free Microemulsion.

Abstract

A surfactant-free microemulsion (SFME) with CO2 stimuli responsive properties was prepared. The oil and the water phases were N, N-dimethylcyclohexylamine (DMCHA) and deionized water, respectively, and N, N-dimethylethanolamine was used as an amphisolvent. The single-phase and multiphase zones were measured by the ternary-phase diagram, and the microstructure of the SFME was determined by measuring the change trend of the electrical conductivity of the system with increasing DMCHA content. While using methyl orange as a probe, the microstructure of the SFME was further confirmed by an UV-visible spectrometer. The microstructures of water-in-oil (SFME-I) and oil-in-water (SFME-II) microemulsions were obtained by changing the DMCHA content in the system. The SFME-I system has a significant phase separation after the action of CO2. However, with the continuous introduction of CO2, the upper phase of DMCHA is gradually protonated and dissolves in the aqueous phase, resulting in a gradual decrease in the volume of the upper phase, and eventually in an aqueous solution of ammonium bicarbonate. For SFME-II, CO2 does not directly cause phase separation, but eventually it becomes an aqueous solution of ammonium bicarbonate with the addition of CO2. Both the water-in-oil structure SFME-I and the oil-in-water structure SFME-II have excellent CO2 stimuli responsive performance.