Atomistic Mechanism of Anisotropic Heat Conduction in the Liquid Crystal 4-Heptyl-4′-cyanobiphenyl: All-Atom Molecular Dynamics

Abstract

All-atom molecular dynamics simulations were performed on 4-heptyl-4′-cyanobiphenyl (7CB) to study the mechanism of heat conduction in this nematic liquid crystal atomistically. To describe 7CB properly, the AMBER-type force field was optimized for the dihedral parameter of biphenyl and the Lennard-Jones parameters. The molecular dynamics calculation using the optimized force field well reproduced the experimental values of the isotropic-nematic phase transition temperature, density, and anisotropy of the thermal conductivity. Furthermore, the contributions of convection, intramolecular interaction, and intermolecular interaction to the thermal conductivity were determined by performing thermal conductivity decomposition analysis. According to the analysis, the contributions of convection, bond stretching, and bond bending interactions were higher in the direction parallel to the nematic director than that perpendicular to the director, which is the origin of the anisotropy in the nematic phase. This result indicates that the anisotropy is caused by well-aligned covalent bonds and high mobility parallel to the director. This quantitative description of the mechanism of heat conduction of 7CB is foreseen to provide new insights toward designing highly thermally conductive liquid-crystalline materials.

Design and synthesis of poly(arylene ether sulfone)s with high glass transition temperature by introducing biphenylene groups

“…Due to the existence of ring structures and interchain π – π stacking, large interchain energy density and steric effects suppress segmental rotation in polymers with rigid biphenylene backbones. The lower probability of segmental rotation reduces disorder scattering 5,17,27 . Therefore, the rigid biphenylene backbones can suppress segmental rotation and enable high thermal conductivity and good thermal stability.…”

“…The lower probability of segmental rotation reduces disorder scattering. 5,17,27 Therefore, the rigid biphenylene backbones can suppress segmental rotation and enable high thermal conductivity and good thermal stability. In addition, the difference in thermal conductivity between the two PAESs can be attributed to the more orderly molecular chain structure of BDS-PES.…”

“…As a rigid rod-like mesogenic unit with simple structure, the biphenylene group has excellent stability and symmetry of molecular structure, and it is widely used as the main structure in liquid crystal polymers. [3][4][5] The introduction of rigid groups into polymer chains is a general method for improving the mechanical and thermal properties of polymers. [6][7][8] Because of its excellent stability and molecular designability, the biphenylene group has attracted much attention and it is an ideal rigid group for molecular design.…”

“…As a rigid rod‐like mesogenic unit with simple structure, the biphenylene group has excellent stability and symmetry of molecular structure, and it is widely used as the main structure in liquid crystal polymers 3–5 . The introduction of rigid groups into polymer chains is a general method for improving the mechanical and thermal properties of polymers 6–8 .…”

Thermal conductivity of benzothieno-benzothiophene derivatives at the nanoscale

“…The BTE approach is known to be far much prohibitive in terms of computational cost than MDbased techniques. Thus, κ of a few molecules ( pentacene, C 60 , PCBM, H 2 Pc, TPD,…) [30][31][32][33][34][35][36][37][38] have been essentially calculated by various methods belonging to the "MD-class" in order to estimate the anisotropy of κ along the long axis of the molecules versus in the perpendicular intralayer directions.…”