Low viscosity reversed hexagonal mesophases induced by hydrophilic additives

This study reports on the formation of a low viscosity H_II mesophase at room temperature upon addition of Transcutol (diethylene glycol mono ethyl ether) or ethanol to the ternary mixture of GMO (glycerol monooleate)/TAG (tricaprylin)/water. The microstructure and bulk properties were characterized in comparison with those of the low viscosity Hn mesophase formed in the ternary GMO/TAG/water mixture at elevated temperatures (35-40°C). We characterized the role of Transcutol or ethanol as inducers of disorder and surfactant mobility. The techniques used were rheology, differential scanning calorimetry (DSC), wide- and small-angle X-ray scattering (WAXS and SAXS, respectively), NMR (self-diffusion and ²H NMR), and Fourier transform infrared (FTIR) spectroscopies. The incorporation of either Transcutol or ethanol induced the formation of less ordered H_II mesophases with smaller domain sizes and lattice parameters at room temperature (up to 30°C), similar to those found for the GMO/TAG/water mixture at more elevated temperatures (35-40°C). On the basis of our measurements, we suggest that Transcutol or ethanol causes dehydration of the GMO headgroups and enhances the mobility of the GMO chains. As a result, these two small molecules, which compete for water with the GMO polar headgroups, may increase the curvature of the cylindrical micelles and also perhaps reduce their length. This results in the formation of fluid H_II structures at room temperature (up to 30°C). It is possible that these phases are a prelude to the H _II-L₂ transformation, which takes place above 35°C.