Nematic ordering of model racemic mixture of stiff trimer chains

Abstract

The nematic ordering of (1) a racemic mixture and (2) an enantiopure melt of trimer chains is inspected within the Landau theory of phase transitions. Each chain contains three rigid segments; consecutive segments are connected at an external angle ν while the planes of the first two and the last two segments form the dihedral angle φ. It is assumed that the rigid segments comprise monomer units. The Landau–de Gennes expansion of the free energy of the melt has been obtained up to the sixth order in powers of the nematic order parameter, the coefficients of this expansion have been calculated from the microscopic model of trimer molecule. It is found that phase diagrams for a racemic mixture may contains the regions of stability of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases depending on the values of angles ν,φ, and monomer unit fractions of rigid segments that characterize the architecture of a trimer chain. In turn, a chiral nematic states are found for an enantiopure melt, depending on the architecture of the chains.