Gelling Lamellar Phases of the Binary System Water-Didodecyldimethylammonium Bromide with an Organogelator

Does the presence of a gel network influence the properties of a lyotropic liquid crystal? Does the replacement of oil by a lyotropic liquid crystal influence the properties of an organogel? To answer these questions we study gelled lyotropic liquid crystals (LLC). In the present study we show that it is possible to gel the lamellar phase of the binary system water-didodecyl dimethylammonium bromide (2C₁₂DAB) with the organogelator 12-hydroxyoctadecanoic acid (12-HOA). We compare various properties of the gelled LLC phases with the "parent systems", i.e., with the binary organogel consisting of n-decane-12-HOA and with the nongelled LC phases, respectively. Optical and electron microscopy, differential scanning calorimetry (DSC), rheometry, as well as small and wide-angle X-ray scattering (SWAXS) proved the coexistence of an L_α phase and a 12-HOA gel network in the gelled L_α phase. However, a small influence of the L_α phase on the gel properties was seen, namely slightly lower sol-gel transition temperatures and viscoelastic moduli of the gelled L_α phase compared to the binary gel. On the other hand, the presence of the gel also has an influence on the L_α phase: the interlayer spacing of the surfactant bilayers in the gelled L_α phases is slightly larger compared to the nongelled L_α phases, which is due to mixing part of the 12-HOA molecules in the L_α bilayers. Despite this mutual influence the structures of both the L_α phase and the gel network are hardly disturbed in the gelled L_α phase, i.e., that the self-assembly of the surfactant and of the gelator molecules clearly occur in an orthogonal way.