Structure of microemulsions in the continuous phase channel

Abstract

We have studied the microemulsion and lamellar phases of two of the most commonly described systems based on nonionic C12E5 and ionic AOT surfactants. We show that C12E5 is best described by the symmetric disordered open connected lamellar model (DOC-lamellar), contrary to the more commonly employed standard flexible model. In the case of AOT, the bicontinuous microemulsion structure is best described by the standard flexible model at high temperatures. Around room temperature, connected cylinders in a molten cubic crystal phase are the only description which corresponds to the data. In the lamellar phase, around one third of the available surface area is lost in fluctuations and defects. Comparing structurally predictive models with results from conductivity measurements show that salt adsorption in the hydrated ethoxy groups is dominant for C12E5 (nonionic). For AOT, our conductivity measurements clarify the role of tortuosity versus cation absorption.