The relationship between rheology and dynamic light scattering for a xylene/water/ButOH/C12E9 microemulsion

Polyethoxylated alkyl compounds consist in a surfactant class that, apart from having a broad application in many fields, yields self-assembled clusters with peculiar geometries: the worm-like micelles. In this work a microemulsion consisting of xylene, water, butanol, and nonaethyleneglycol-monododecylether was studied using rheometry and dynamic light scattering. Zero-shear rate viscosity-temperature dependence had a peculiar Arrhenius character, with the occurrence of two apparent flow activation enthalpies, a higher one below 25 °C, and a lower one above this very temperature. KWW equation was fitted to intensity correlation function data obtained from dynamic light scattering experiments at different temperatures. The temperature dependence of KWW-related parameters indicated that the change in flow activation enthalpy could be related to a change in micelle morphology.

A drastic change in apparent flow activation enthalpy (the slope of lnη0versus 1/T curve) indicates a transition between nanodrop/worm-like geometries.Figure optionsDownload as PowerPoint slideHighlights
► Viscosity of a microemulsion has an Arrhenius-type dependence on temperature.
► Arrhenius dependence has two activation enthalpies, above and below a critical temperature.
► DLS suggests relaxation is governed by 2 relaxation rate distributions (2 KWW functions).
► Parameters from KWW equation have abrupt changes above and below same critical temperature.
► Changes related to increase/decrease of worm-like structures as a function of temperature.