Stabilisation of cosmetic compositions using combined emulsifiers

Abstract

Objectives.This study investigated the surface properties and micelle formation of combinedstabilizers, which are a mixture of ionic and nonionic surfactants or different nonionic surfactants,to establish a correlation between the composition of stabilizers and the colloidal–chemicalproperties of direct emulsions obtained in their presence.Methods.The surface tension at the interface between the aqueous solutions of the combinedstabilizers with air and toluene was measured using a digital tensiometer. The sedimentationstability of the emulsions was assessed by the volume of the exfoliated water and oil phasesfor seven days. The particle sizes of the dispersed phase were determined using an OlympusCX3 bright field microscope equipped with a universal serial bus video camera connection. Therheological properties of the emulsions were evaluated using a rotary viscometer.Results.According to the isotherms of the surface tension of aqueous surfactant solutions atthe interface with air and toluene at emulsion preparation temperatures of 50 °C and 65 °C,a mixture of nonionic surfactants exhibited a higher surface activity and lower critical micelleconcentration at the interface with toluene. The optimal amount of stabilizers providing stabilityto the compositions for one month was 4 mass % for a mixture of anionic surfactants and nonionicsurfactants and 7 mass % for mixtures of different nonionic surfactants. Emulsions obtained in thepresence of a mixture of anionic and nonionic surfactants exhibited higher kinetic sedimentationstability values due to the formation of electrostatic and steric stabilization factors in the system.The developed compositions were microheterogeneous systems, the average droplet diameter ofwhich varied within the range of 1.0–5.7 µm. In terms of rheological properties, emulsions wereclassified as liquid-like structured systems with coagulation structures; the strength of singlecontacts between particles of the dispersed phase was (1.6–27.0) × 10-10N.Conclusions.A comparison of the physicochemical characteristics of the compositions obtainedin the presence of organic emulsifiers showed that emulsions stabilized using a mixture of ionicand nonionic surfactants, which form mixed adsorption layers, exhibited the best set of properties.