Formation and Characterization of Fully Dilutable Microemulsion with Fatty Acid Methyl Esters as Oil Phase

Abstract

The objective of this study was to develop a green microemulsion with potential applications in the delivery system for oil-soluble solid active ingredients. A microemulsion was prepared using fatty acid methyl esters (FAMEs) as the oil phase, a mixture of alkyl polyglycoside (APG) and alkylpolyethoxy carboxylates (AEC) as the surfactant, and alkanol as a cosurfactant. The feasibility of formulating a fully water dilutable microemulsion with a green surfactant and nontoxic oil phase has been demonstrated. Pseudoternary phase diagrams were constructed by titration, and a large isotropic region was found. To expand the isotropic regions area, the effect of the mixing ratio of APG and AEC, the chain length of the cosurfactant and the oil on the isotropic area of the phase diagram were investigated systematically. As the water content increased, the continuous structural transition from water-in-oil, bicontinuous to oil-in-water microemulsion was followed by monitoring conductivity. Percolation phenomena were observed during this process. Based on the phase behavior study, the optimum formulations were chosen from isotropic regions with a minimum amount of surfactants, which were able to be fully diluted with water. The dilute microemulsion was studied by dynamic light scattering (DLS), dynamic contact angle and dynamic surface tension. The DLS result revealed that the main destabilization mechanism for these dilute microemulsion was Ostwald ripening at the beginning of the dilution process. Dynamic contact angle and dynamic surface tension results demonstrated the dilute microemulsion exhibited excellent wetting and spreading properties on hydrophobic surfaces.