SAXS and Rheometry Studies of Diglycerol Monolurate Reverse Micelles in Styrene

Abstract

We have investigated the structure and rheology of diglycerol monolaurate (C(12)G(2)) reverse micelles in styrene using small-angle X-ray scattering (SAXS) and rheometry techniques. The SAXS data have been evaluated by generalized indirect Fourier transformation (GIFT) method and further supported by geometrical model fittings. We found that the C(12)G(2) when added into styrene spontaneously self-assemble into ellipsoidal prolate type reverse micelles under ambient conditions. Micelles grew and micellar aggregation number (N(agg)) increased with the increase in surfactant concentration demonstrating concentration induced one dimensional micellar growth, which was further supported by rheology data; the relative viscosity, η(r), for the C(12)G(2)/styrene mixtures exhibit far steeper concentration dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger-Dougherty relation, due to the elongated micellar structures. On the other hand, a distinct modulation in the shape and size of micelles favoring ellipsoidal prolate-to-sphere type transition was observed upon heating, whose scheme could be attributed to the enhanced penetration tendency of oil into the lipophilic shell of the surfactant at the higher temperatures. As anticipated reverse micelles swelled with water causing two dimensional micellar growth; both the maximum dimension and maximum core radius increase with water.