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 ≤ xQL13-6 ≤ 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.
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 TAC by the reduction factor R according to the equation:
R = δ(T)/θopt(T) = cos−1 [dC(T)/dAC]/θopt(T)
where δ is the tilt angle required to give the observed layer contraction dC(T)/dAC assuming a model of hard spherocylinders in which the layer contraction scales with the cosine of the tilt angle, and θopt is the observed tilt angle measured by polarised optical microscopy [Citation17].