Design of liquid crystals with 'de Vries-like' properties: the effect of an ethynyl spacer in the core structure. Issue 6 (3rd May 2019)

• Record Type: Journal Article
• Authors: Ahmed, Ziauddin; Müller, Carsten; Johnston, Jaya J.; Nguyen, Kevin; Schubert, Christopher P. J.; Abitaev, Karina; Marino, Sebastian; Giesselmann, Frank; Lemieux, Robert P.
• Is Part Of: Liquid crystals. Volume 46:Issue 6(2019)
• Page Start: 896
• Page End: 904
• Publication Date: 2019-05-03
• Subjects: Liquid crystal -- tricarbosilane -- de Vries-like -- orientational order -- effective length -- interdigitation; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2018.1536810
• Languages: English
• ISSNs: 0267-8292

Abstract

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 mesogensQL16-6 andQL17-6 . 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 S 2 in the SmA phase. The tricarbosilane-terminated mesogensWL41-5 andWL42-6 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 neitherWL41-5 ( R = 0.49) norWL42-6 ( R = 0.80) exhibit 'de Vries-like' properties. The S 2 ( 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 L eff ( T ) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S 2 in compensating for the molecular tilt. Graphical Abstract: