Abstract: An oil-in-water microemulsion of increased viscosity is disclosed, which microemulsion comprises an aqueous continuous phase, an oil phase, a primary surfactant having a lipophilic moiety and a hydrophilic moiety, wherein the hydrophilic moiety carries an electrostatic charge and a cosurfactant. The viscosity is increased by adding a secondary surfactant which is characterized by a long chain lipophilic moiety and a charged hydrophilic moiety which is reactive with the charged hydrophilic moiety of the primary surfactant. In forming the microemulsion of increased viscosity, the microemulsion is formed first in the absence of the secondary surfactant, and the secondary surfactant is added thereto.

Abstract: A unique method for the preparation of oil-in-water microemulsions is described. In carrying out this method, microemulsions are prepared in a four-step process: (1) a surfactant is selected which is just barely soluble in the oil phase; (2) the surfactant thus selected is dissolved in the oil to be emulsified in an amount effective to yield a fine emulsion of the emulsified oil in an aqueous phase; and (3) the oil, together with its dissolved surfactant, is added to the water phase and shaken or stirred; and (4) finally, there is provided a second surfactant in the water phase which is somewhat more soluble in water than the first surfactant to produce a substantially clear microemulsion of oil in water.