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

• Published in: Journal of molecular liquids 2023-08, Vol.384, p.122222, Article 122222
• Main Author: Aliev, M.A.
• Format: Article
• Language: English
• Subjects: Bent-shaped liquid crystals; Biaxial nematic phase; Landau–de Gennes free energy; Semiflexible polymer
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.122222

The nematic ordering of a melt of V-shaped molecules composed of two semiflexible arms connected by one end at an external angle α 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 (NU−) 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 α and the sequence of phase transitions I−NU−−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−NU−, and NU+−NU− 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 NU−−NB transition in the phase diagrams in certain intervals of values of the stiffness parameter. •Microscopic model of V-shaped particle with flexible arms is proposed.•Molecular architecture and stiffness of the arms strongly influence the phase behavior.•Re-entrant uniaxial and biaxial phases are found in phase diagrams.•Tricritical points appear for certain ranges of values of the stiffness parameter.