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a substance that facilitates emulsification and imparts stability to emulsions. The ability of emulsifiers to emulsify results from their capacity to accumulate on the boundary of two liquid phases, thus lowering the interphase tension, and to create a protective layer around the droplets, thus preventing coagulation and coalescence. The principal types of emulsifiers are soaps, soaplike surfactants, soluble compounds of high molecular weight, and highly dispersed solids.
A rule of thumb in the selection of emulsifiers is that soluble emulsifiers are always more soluble in the dispersion medium than in the dispersed phase and that insoluble solid emulsifiers are similarly better wetted by the dispersion medium. Therefore, sodium oleate, polyvinyl alcohol, and hydrophilic clay minerals, such as bentonites and kaolin, are suitable for producing oil-in-water emulsions, and metal soaps, carbon black, and substances containing asphalt and tar are suitable for producing water-in-oil emulsions (seeHYDROPHILIC AND HYDROPHOBIC CAPACITY). Mixtures are usually more effective emulsifiers than pure substances and are more often used as components of emulsions.
L. A. SHITS