NEMATIC ORDERING AND MICROPHASE SEGREGATION IN A DIBLOCK POLYMER-LIQUID-CRYSTAL-POLYMER

A theory of nematic ordering and microphase segregation in an incompre ssible melt of AB diblock copolymers is developed for the case when th e A block is a polymer composed of Na monomers and the B block is a ma in-chain liquid crystal polymer composed of Ng freely jointed nematoge ns. Isotropic monomer-nematogen interactions are characterized by a Fl ory parameter chi, and anisotropic nematogen-nematogen interactions ar e characterized by a Maier-Saupe parameter J. Long chains (N-A,N-B >> 1) in the strong segregation limit (chi(N) >> 1, with N = N-A + N-B) a re considered. An approximate free energy of the melt is given for the following segregation morphologies: homogeneous, lamellar, cylindrica l micelles, and spherical micelles. The free energy is minimized to de termine the equilibrium morphology, lattice constant, and degree of ne matic order as a function of chi(N), J, and N-A/N. Both morphological and isotropic-nematic transitions occur, and the ordinary diblock copo lymer phase diagram is significantly altered.