Visco-elastic properties of multi-component mixtures of hockey stick-shaped liquid crystal compounds

Abstract

Measurements of optical birefringence (Δn), permittivity (ε||, ε⊥), splay elastic modulus (K11) and rotational viscosity (γ1) have been carried out on the nematic (N) phase of a few multi-component liquid crystal mixtures having the hockey stick-shaped 4-(3-n-alkyloxy-2-methyl-phenyliminomethyl)phenyl 4-n-alkyloxycinnamate compounds. Three eutectic mixtures (tri-, tetra- and penta-component) were prepared using the Le Chatelier, Schröder and Van Laar (CSL) equation. The nematic range in all the investigated mixtures has been found to be relatively greater than that in most of the pure components. The Δn values have been found to be comparatively smaller than those for the constituent compounds. A temperature dependent inversion in the static dielectric anisotropy (Δε = ε|| − ε⊥) has been observed for all the mixtures on entering the anticlinic smectic-C (Sm-Ca) phase. No trace of pretransitional divergence has been detected in the temperature dependence of K11 in vicinity of the nematic to lower smectic-C transition. At a fixed reduced temperature, the γ1 values are either slightly higher or close to those of the pure compounds. The outcomes are explained in the framework of influence of molecular structure on the phase behaviour of multi-component mesogenic system.