Molecular Simulation Approaches to the Study of Thermotropic and Lyotropic Liquid Crystals

Abstract

Over the last decade, the availability of computer time, together with new algorithms capable of exploiting parallel computer architectures, has opened up many possibilities in molecularly modelling liquid crystalline systems. This perspective article points to recent progress in modelling both thermotropic and lyotropic systems. For thermotropic nematics, the advent of improved molecular force fields can provide predictions for nematic clearing temperatures within a 10 K range. Such studies also provide valuable insights into the structure of more complex phases, where molecular organisation may be challenging to probe experimentally. Developments in coarse-grained models for thermotropics are discussed in the context of understanding the complex interplay of molecular packing, microphase separation and local interactions, and in developing methods for the calculation of material properties for thermotropics. We discuss progress towards the calculation of elastic constants, rotational viscosity coefficients, flexoelectric coefficients and helical twisting powers. The article also covers developments in modelling micelles, conventional lyotropic phases, lyotropic phase diagrams, and chromonic liquid crystals. For the latter, atomistic simulations have been particularly productive in clarifying the nature of the self-assembled aggregates in dilute solution. The development of effective coarse-grained models for chromonics is discussed in detail, including models that have demonstrated the formation of the chromonic N and M phases.

Study of the Experimental and Simulated Vibrational Spectra Together with Conformational Analysis of Thioether Cyanobiphenyl-Based Liquid Crystal Dimers

“…Current experimental results show that the formation of the N TB phase is very sensitive to changes in the shape of the molecules [ 52 , 53 , 54 , 55 , 56 , 57 ]; therefore, the key is to carefully define the relationship between the molecular parameters of the molecules and the occurrence of the modulated nematic phase. For this purpose, many authors have used molecular modeling methods, mainly the density functional theory (DFT) [ 28 , 29 , 33 , 34 , 52 , 58 , 59 , 60 , 61 ] or molecular dynamics simulations (MD) [ 62 , 63 , 64 ] to analyze structural and conformational changes of the dimers. However, no analysis of the conformational changes of molecules in the transition from the nematic to the twist-bend nematic phase based on a comparison of simulated and experimental vibrational spectra has been performed so far.…”

Impact of Molecular-level Structural Disruption on Relaxation Dynamics of Polymers with End-on and Side-on Liquid Crystal Moieties

“…11 These applications include, among others, solar cells, 12 conductors, 13 3D-printed shape-changing materials with hierarchical structures and complex geometries, 14−16 and soft robotics components. 17−25 The classic mesophases formed by ordinary liquid crystals, such as nematic, smectic A, smectic B, etc., 26,27 are maintained in these hybrid molecules due to the flexibility of the polymers and the decoupling of the stiff LC moieties from the polymer backbones by sufficiently long spacers. This provides the necessary independent movement of molecules, which facilitates proper alignment.…”

“…conductors, 13 3D-printed shape-changing materials with hierarchical structures and complex geometries, 14−16 and soft robotics components. 17−25 The classic mesophases formed by ordinary liquid crystals, such as nematic, smectic A, smectic B, etc., 26,27 are maintained in these hybrid molecules due to the flexibility of the polymers and the decoupling of the stiff LC moieties from the polymer backbones by sufficiently long spacers. This provides the necessary independent movement of molecules, which facilitates proper alignment.…”