Formulation and characterization of microemulsions based on mixed nonionic surfactants and peppermint oil

摘要

Water/sucrose laurate/ethoxylated mono-di-glyceride/ethanol/peppermint oil microemulsion systems were formulated and characterized using electrical conductivity, dynamic viscosity, nuclear magnetic resonance, dynamic light scattering, small angle X-ray scattering and cryogenic transmission electron microscopy. The solubilization capacity of water in the oil is dependent on the surfactants and ethanol/oil mixing ratios (w/w). Static percolation phenomena were observed in these systems, and the water volume fraction percolation threshold was determined. A progressive transformation of the water-in-oil to bicontinuous and inversion to oil-in-water microemulsions occurs upon dilution with water, which was revealed by the determination of the diffusion coefficients of both oil and water inside the microemulsions. The diffusion coefficients of the surfactants at the interface of the microemulsions increase with increasing water volume fraction. The periodicity of the microemulsions increases linearly with increasing water volume fraction. In addition, the correlation length increases with water volume fraction to a certain value then decreases. Cryo-TEM images of the oil-in-water microemulsions revealed the presence of spheroidal droplets of up to 12 nm diameter.