Structural Relations Between Lyotropic Phases in the Vicinity of the”Nematic” State
Some lyotropic mesophases are anisotropic fluids certain properties of which, orientation in a magnetic field, textures, are similar to those of thermotropic nematics. On the other hand, as for any lyotropic liquid crystals, they must be assemblies of aggregates of amphiphilic molecules but their organizations must differ from those studied so far in classical lyotropic liquid crystals. As a matter of fact in the latter case, anisotropy is only known for viscous well-ordered phases (lamellar or cylindrical) and fluidity is only associated with disordered phases (micellar). A recent X-ray diffraction study of the lyotropic “nematic” phases obtained with the mixture sodium decyl sulfate (SDS)-decanol-water  shows that the structural elements of these phases are disc or cylinder shaped aggregates, according to the temperature and the composition. The aggregates are organized with orientational order but without long range translational order.