Effect of flexibility of arms on the nematic ordering of V-shaped molecules

The nematic ordering of a melt of V-shaped molecules composed of two semiflexible arms connected by one end at an external angle ������ is inspected within the Landau theory of phase transitions. The conformational statistics of arms is described by a discrete worm-like chain model. It is found that for a sufficiently high stiffness of the arms the phase diagram contains the regions of stability of isotropic (I), prolate (Nu) and oblate (N-U) uniaxial, and biaxial (NB) nematic phases. The isotropic-uniaxial nematic and uniaxial nematic - biaxial nematic phase transitions are of the first and second order, respectively. At lowering the stiffness of arms the stability area of NB phase decreases; the re-entrant NB phase becomes possible in the certain range of angles ������ and the sequence of phase transitions I - N-U - NB - Nu - NB occurs. At a sufficiently low stiffness, the stability region of the nematic biaxial phase disappears completely, and phase diagrams display only the first order transitions between I - Nu, I - N-U, and Nu - N-U phases. A further decrease in the stiffness of arms leaves only the first order I - Nu transition in the phase diagrams. The tricritical points appear at the curves of N-U - NB transition in the phase diagrams in certain intervals of values of the stiffness parameter.

Automated summary

The nematic ordering of V-shaped molecules with two semiflexible arms connected by one end at an external angle is investigated using the Landau theory of phase transitions. The phase diagram shows stable regions of isotropic, prolate uniaxial, oblate uniaxial, and biaxial nematic phases. The phase transitions from isotropic to uniaxial and from uniaxial to biaxial nematic are of the first and second order, respectively. The stability area of the biaxial phase decreases with decreasing arm stiffness and a re-entrant biaxial phase is possible in a certain range of angles. The tricritical points appear at the curves of the uniaxial to biaxial nematic transition in the phase diagrams within certain intervals of the stiffness parameter.