A surfactant-free microemulsion containing diethyl malonate, ethanol, and water: Microstructure, micropolarity and solubilizations

The microstructure, micropolarity and solubilizations of a surfactant-free microemulsion (SFME) containing diethyl malonate (DEM), ethanol (EtOH), and water were investigated in details. The ternary phase diagram of the SFME was constructed, and the single-phase region of the diagram was divided into oil in water (O/W), bicontinuous (B.C.), and water in oil (W/O) subregions. The dynamic light scattering (DLS) results showed that there is an orderly microstructure in each subregion of the system. The UV-vis absorbance spectra of CoCl2 indicated the formation of complete W/O SFME droplets, when the water content is relatively large. With an increase in water content, the association between Cu2+ and water molecules increases, resulting in a red shift of the UV-vis absorbance spectra of CuCl2. The solubilization of K3Fe(CN)(6) in the W/O SFME was investigated, and found that the SFME has better solubilization effect on inorganic salts. Riboflavin also has a strong solubilizing effect in the W/O SFME, and the absorbance conforms to Lambert-Beer's law. When the water content is small, the absorbance deviates from Lambert-Beer's law. This is in agreement with the results of the solubilization of CoCl2. A complete W/O SFME could be formed when the water mass fraction (w) exceeds 0.10. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.