Lyotropic mesomorphism of AB block copolymers in nematic solvents

An AB block copolymer consisting of a liquid crystalline block A and an iso tropic block B has been selectively dissolved in a low molecular weight nem atic solvent (LMWNS). We investigated mixtures with fixed weight fractions using polarizing optical microscopy, small angle X-ray scattering (SAXS), s mall angle neutron scattering (SANS) and H-2 NMR spectroscopy. The informat ion obtained from the different methods that are selectively for the mesoge n or micellar ordering (or for both) enables us to present the complete pha se diagram. The A block of the copolymer is miscible in the nematic solvent and thus is termed "nematophilic" while the other constituent block is "ne matophobic". We show that these block copolymers in a nematic solvent behav e like polymeric surfactants in aqueous solution. Here, the concept of amph iphilicity can be extended to a non-aqueous anisotropic system. Cylindrical micelles are formed in the diluted regime. At higher concentrations the mi celle form nematic and hexagonal: phases. Thus, this highly complex system contains two different anisotropies: The superstructures of the anisotropic micelles and the ordering of the mesogens within (or around) the micelles.