Comparative study of local structure of two cyanobiphenyl liquid crystals by molecular dynamics method

Abstract

Fully-atomistic molecular dynamics simulations were carried out on two similar cyanobiphenyl nematogens, HO-6OCB and 7OCB, in order to study effects of hydrogen bonds on local structure of liquid crystals. Comparable length of these two molecules provides more evident results on the effects of hydrogen bonding. The analysis of radial and cylindrical distribution functions clearly shows the differences in local structure of two mesogens. The simulations showed that anti-parallel alignment is preferable for the HO-6OCB. Hydrogen bonds between OH-groups are observed for 51% of HO-6OCB molecules, while hydrogen bonding between CN- and OH-groups occurs only for 16% of molecules. The lifetimes of H-bonds differ due to different mobility of molecular fragments (50 ps for N⋅⋅⋅H-O and 41 ps for O⋅⋅⋅H-O). Although the standard Optimized Potentials for Liquid Simulations - All-Atom force field cannot reproduce some experimental parameters quantitatively (order parameters are overestimated, diffusion coefficients are not reproduced well), the comparison of relative simulated results for the pair of mesogens is nevertheless consistent with the same relative experimental parameters. Thus, the comparative study of simulated and experimental results for the pair of similar liquid crystals still can be assumed plausible.

Polymorphism of hydrogen-bonded star mesogens – a combinatorial DFT-D and FT-IR spectroscopy study

“…Dispersion forces between non-covalently bonded molecules or building blocks are crucial to stabilize the mesogenic structure as well as segregation processes to form highly ordered mesophases. [87][88][89] Although many DFT and molecular dynamics studies exist for small covalent LC systems, 80,[90][91][92][93][94][95][96][97] giving reasonable explanation of their structural diversity, a computational study of hydrogen-bonded system has not been reported so far. To get a deeper understanding of such supramolecular materials those studies would be highly valuable.…”

15N–13C Dipole Couplings in Smectic Mesophase of a Thermotropic Ionic Liquid

“…Molecular motion and geometry considerations can be used to reveal the signs of the dipolar couplings and separate dipolar and J -coupling contributions. For this, details of complex anisotropic molecular rotations are required and they can be provided, for example, by MD simulation [ 31 ]. However, in the present methodological work, such an analysis was not attempted.…”

Optical and calorimetric studies near the smectic-A to smectic-C tricritical point

“…This article principally devoted focusing on the optical and calorimetric investigation in a binary system comprising a hockey-stick-shaped molecule (H-22.5) [9,11,45] and a calamitic compound (7OCB) [46][47][48] from high-resolution birefringence (Δn) and specific heat capacity (ΔC P ) measurements, in order to extract the critical behavior near the Sm-A-Sm-C phase transition. Both techniques yield adequate data points near the phase transition and therefore, able to analyze the Sm-A-Sm-C phase transitional anomaly.…”