Structure and phase behaviour of a lyotropic mesophase system: cellulose tricarbanilate-methyl acetoacetate

Abstract

Solutions of cellulose tricarbanilate (CTC) in methyl acetoacetate (MAA) have been investigated and cholesteric mesophases found above a certain concentration. Structural features as well as the phase behaviour of this lyotropic liquid crystalline system were studied. The pitch of the helicoidal cholesteric structure P decreases with higher concentration c as Pαc −m with m = 2.3. The exponent can be correlated with the chain stiffness of the cellulosic molecule. The temperature behaviour of the pitch is in agreement with the theoretical considerations of others, if a left-handed helix conformation of a single cellulosic molecule is assumed. It can also be concluded that both steric and polar effects cause the formation of the mesophase. The thermally induced cholesteric-isotropic phase transition is a first-order transition. A two-phase region separates the anisotropic and isotropic phase ranges. The beginning of the transition as well as the clearing point are shifted to higher temperatures with increasing concentration. The resulting phase diagram is qualitatively best described by the lattice theory of Flory and Warner. The higher thermotropic effect as compared to the theory is correlated to a decrease in the Kuhn segment length. The enthalpy of the phase transition rises with increasing CTC concentration and can be explained by the disappearance of polymer-polymer interactions in favour of polymer-polymer contacts.