Phase diagram of a model melt of bent--core molecules

Abstract

ABSTRACT The Landau theory of phase transitions with single-order parameter (second rank alignment tensor) has been applied to study the formation of modulated nematic phases in a melt of the symmetric V-shaped molecules. The arms of V-shaped molecule are modelled by rod-like segments composed of monomer units. Molecular architecture is determined by an external angle between arms. The coefficients of the Landau–de Gennes free energy of melt have been found from microscopic model of V shaped particle. The phase diagram of the system contains regions of stability of the isotropic (), uniform nematic , and modulated nematic phases ( and ). Principal director (the eigenvector of the alignment tensor, which corresponds to the eigenvalue with the largest absolute value) in the phase moves along the helix and forms a fixed acute angle with the helix axis. For the modulated phase the principal director is orthogonal to the helix axis while one of the two remaining directors is parallel to helix axis.