Cone–Plate Rheometer as Reactor and Viscosity Probe for the Detection of Transitional Phase Inversion of Brij30–Isopropyl Myristate–Water Model Emulsion

Brij30/isopropyl myristate/water model emulsions were used to study the inversion morphology change from O/W to W/O. The transitional phase inversion was detected by monitoring the electrical conductivity during a heating–cooling cycle while the viscosity of the emulsion was followed under constant shear rate with a cone–plate rheometer equipment. The two methods provide similar values of phase inversion temperature. However, different rheological profiles are observed depending on the surfactant concentration and water fraction. Viscosity maps of formulation-composition maps (specifically temperature–surfactant concentration and temperature–water fraction) pointed to the occurrence of both transitional and catastrophic inversion processes. A complete formulation–composition map with all different emulsion morphologies and isoviscosities contours for the 9% Brij30/IPM/water is presented. The use of a commercial cone–plate rheometer exhibits several advantages over the classical conductivity measurement; in particular, it does not imply any electrolyte addition in the aqueous phase and requires only a small volume of emulsion.