Tuning the mesomorphic properties of carbosilane-terminated and conventional 2-alkoxy-5-(4-alkoxyphenyl)-1,3,4-thiadiazole liquid crystals as binary mixtures with bimodal length distributions

Abstract

The phase diagrams of binary mixtures of smectic C (SmC) mesogens – the carbosilane-terminated mesogen 2-(6-chlorohexyloxy)-5-(4-(12,12,14,14,16,16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl)-1,3,4-thiadiazole (QL13-6) and one of nine conventional 2-alkoxy-5-(4-alkoxyphenyl)-1,3,4-thiadiazole mesogens (QL14-m/n) – with a molecular length ratio QL13-6/QL14-m/n ranging from 1.24 to 1.46 show the induction of a smectic A (SmA) phase in the mole fraction range 0.1 ≤ x_QL13-6 ≤ 0.6. The results show that the temperature range of the induced SmA phase is remarkably sensitive to the molecular length ratio, and that this approach to tuning the mesomorphic properties of SmA–SmC liquid crystal mixtures may provide a powerful new tool in the formulation of mixtures for SSFLC and electroclinic applications.

Keywords:

• smectic liquid crystal
• carbosilane
• bimodal length distribution
• binary mixture

Notes

1. The degree of ‘de Vries-like’ behaviour in a smectic liquid crystal may be quantified on a scale of 0 (perfect ‘de Vries’) to 1 (conventional SmA–SmC transition) at a given temperature T below T_AC by the reduction factor R according to the equation:

R = δ(T)/θ_opt(T) = cos⁻¹ [d_C(T)/d_AC]/θ_opt(T)

where δ is the tilt angle required to give the observed layer contraction d_C(T)/d_AC assuming a model of hard spherocylinders in which the layer contraction scales with the cosine of the tilt angle, and θ_opt is the observed tilt angle measured by polarised optical microscopy [17].

Additional information

Funding

We thank the Natural Sciences and Engineering Research Council of Canada (Discovery and CREATE Grants) for support of this work.