öljyinvettä

Öljyinvettä, commonly referred to in English as an oil-in-water emulsion, is a dispersion in which oil droplets are dispersed within a continuous water phase. The oil droplets are typically submicron to a few micrometers in diameter and remain suspended by interfacial stabilization. This form contrasts with water-in-oil emulsions, where water droplets are dispersed in oil.

Formation and stabilization: Oil-in-water emulsions are produced by emulsification using mechanical energy such as high-shear mixing, homogenization, or ultrasonication, often in the presence of an emulsifier or surfactant. Emulsifiers adsorb at the oil–water interface, lowering interfacial tension and forming a protective film around droplets. Stabilization can also be achieved by polymers or charged particles that provide steric or electrostatic repulsion to slow coalescence and creaming.

Properties: Droplet size distribution, phase volume ratio, and viscosity determine stability and rheology. Emulsions can be sensitive to temperature, salt concentration, and pH, which may promote coalescence, Ostwald ripening, or phase inversion (to a water-in-oil type under certain conditions).

Applications: Oil-in-water emulsions are common in foods (mayonnaises, dressings), cosmetics (creams, lotions), pharmaceuticals and nutraceuticals, and many cleaning and coating formulations. In environmental contexts, dispersants create oil-in-water emulsions to enhance oil spill dispersion, influencing cleanup strategies.

Measurement and safety: Characterization methods include optical microscopy, dynamic light scattering for droplet size, and rheology for flow behavior. Selection of emulsifiers and processing conditions depends on intended use, regulatory requirements, and environmental impact.