Oil-in water-emulsion gels: determination and mathematical treatment of flow properties.

Flow properties of oil-in-water (o/w)-emulsion gels are determined for two experimental designs using common Searle-type rotating viscometers. Samples were characterized after preparation as well as real time and stress stability testing. Model emulsions contained Newtonian oil phases and cross-linked acrylic acid polymers and carboxymethylcellulose sodium as aqueous thickener. Varying two factors, concentration of gelling agent in the aqueous phase and amount of phase fraction phi, a series of formulations was obtained ranging from liquid o/w-lotions to semi-solid o/w-emulsion gels. Robust data evaluation is done applying Herschel, Bulkley, Van-Wazer (HBW) power law function and determination of rheological area under the curve (AUC) parameters. Factors were calculated by means of a power law function and a modified Taylor-series. Second order multiple regression and the method of Kriging were applied to describe summarized response surfaces. O/w-emulsion gels are (pseudo)plastics without rheotropic effects. Flow properties can be assessed by choosing an appropriate concentration and type of gelling agent. The influence of the Newtonian oil phase vanishes in a dominant thickened aqueous phase. Consistency of liquid o/w-lotions on the other hand is primarily controlled by phi.