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5. Design of liquid crystals with 'de Vries-like' properties: the effect of an ethynyl spacer in the core structure.

Author

Ahmed, Ziauddin, Müller, Carsten, Johnston, Jaya J., Nguyen, Kevin, Schubert, Christopher P. J., Abitaev, Karina, Marino, Sebastian, Giesselmann, Frank, and Lemieux, Robert P.

Subjects
LIQUID crystals, FERROELECTRIC liquid crystals, DIFFERENTIAL scanning calorimetry, MICROSCOPY, X-ray scattering
Abstract

We investigate the origins of 'de Vries-like' liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S2 in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and 'de Vries-like' properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit 'de Vries-like' properties. The S2(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with 'de Vries-like' behaviour. However, the Leff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S2 in compensating for the molecular tilt. [ABSTRACT FROM AUTHOR]

Published
2019
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