microemulsifier

A microemulsifier is a substance or combination of substances that stabilizes microemulsions, typically acting as a surfactant or a mixture of surfactants with cosurfactants. Microemulsions are thermodynamically stable, optically isotropic dispersions of two immiscible liquids (usually oil and water) that form spontaneously under suitable composition and conditions. Microemulsifiers reduce interfacial tension between the phases to very low values and promote the preferred interfacial curvature, enabling the formation of nanoscale droplets and a thermodynamically favorable state.

Common microemulsifiers include nonionic, anionic, cationic, or zwitterionic surfactants, or mixtures thereof. They are often used with cosurfactants such as short-chain alcohols (ethanol, propanol), glycols, or other organics to fine-tune curvature and expand the microemulsion region in phase diagrams. The resulting systems can be oil-in-water, water-in-oil, or bicontinuous, with typical droplet sizes in the range of 5 to 100 nanometers.

Characterization and design frequently involve constructing pseudoternary phase diagrams to locate the microemulsion region and examining properties such as conductivity, transmittance, and droplet size. Advantages of microemulsions include spontaneous formation at ambient conditions, high optical clarity, and potential for enhanced solubilization and delivery of active ingredients.

Applications span pharmaceuticals, cosmetics, food, and agrochemicals, where microemulsifiers aid in achieving uniform dispersion, improved stability, and controlled release. Limitations can include formulation sensitivity to temperature, salinity, or ingredient toxicity, requiring careful selection and testing of components.