Nemato-elasticity of hybrid molecular-colloidal liquid crystals

TL;DR

This paper presents a theoretical analysis of the elastic properties of hybrid molecular-colloidal liquid crystals, highlighting how colloidal rods influence nematic elasticity and providing estimates for all elastic moduli in various symmetries.

Contribution

It offers a comprehensive theoretical framework for understanding the elastic moduli in hybrid liquid crystals with different symmetries, including experimental validation for uniaxial systems.

Findings

Colloidal rods significantly increase splay elasticity in uniaxial systems.

Quantitative agreement between theory and experiment for splay elasticity.

Identification of key elastic moduli relevant for orthorhombic hybrid liquid crystals.

Abstract

Colloidal rods immersed in a thermotropic liquid-crystalline solvent are at the basis of so-called hybrid liquid crystals which are characterized by tunable nematic fluidity with symmetries ranging from conventional uniaxial nematic or anti-nematic to orthorhombic [Mundoor et al., Science 360, 768 (2018)]. We provide a theoretical analysis of the elastic moduli of such systems by considering interactions between the individual rods with the embedding solvent through surface-anchoring forces, as well as steric and electrostatic interactions between the rods themselves. For uniaxial systems the presence of colloidal rods generates a marked increase of the splay elasticity which we found to be in quantitative agreement with experimental measurements. For orthorhombic hybrid liquid crystals we provide estimates of all twelve elastic moduli and show that only a small subset of those elastic constants play a relevant role in describing the nemato-elastic properties. The complexity and possibilities related to identifying the elastic moduli in experiments are briefly discussed. The results are expected to be helpful in stimulating future studies on defect-dressed "topological" colloids and the analysis of boundary-driven phenomena where the non-trivial director topology generated by biaxial nematics plays a key role.