Structure and rheology of direct and reverse liquid-crystal phases in a block copolymer/water/oil system

A comparative study on rheology and microstructure of direct and reverse liquid-crystal phases in a single-block copolymer/oil/water system using rheometry and small-angle X-ray scattering (SAXS) is presented. The microstructure of reverse phases is less sensitive to an increase in temperature, since changes in surface curvature are limited, whereas in the case of direct phase, a decrease in the effective surface area promotes structural transitions. The studied hexagonal and micellar cubic phases show gel-like behavior under the experimental conditions used, but the values of the plateau elastic modulus are one order the magnitude higher for micellar cubic phases. Rheological parameters show values of the same order of magnitude for reverse and direct phases of same morphology, although direct phases show slightly higher elastic modulus and complex viscosity, probably reflecting the effect of the continuous phase. In some cases, a correlation between rheology and microstructural changes was found.