Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers. Issue 1 (2nd January 2017)

• Record Type: Journal Article
• Authors: Cukrov, Greta; Mosaddeghian Golestani, Youssef; Xiang, Jie; Nastishin, Yu. A.; Ahmed, Z.; Welch, C.; Mehl, G. H.; Lavrentovich, Oleg D.
• Is Part Of: Liquid crystals. Volume 44:Issue 1(2017)
• Page Start: 219
• Page End: 231
• Publication Date: 2017-01-02
• Subjects: Dimeric nematic -- elastic constants -- birefringence -- negative dielectric anisotropy -- twist-bend nematic; Liquid crystals -- Periodicals; 548.905
• DOI: 10.1080/02678292.2016.1240248
• Languages: English
• ISSNs: 0267-8292

Abstract

ABSTRACT: We report temperature dependencies of material properties such as dielectric anisotropy, birefringence, splay ( ), twist ( ), and bend ( ) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behaviour to that of a corresponding monomer MCT5. DTC5C9 forms a twist-bend nematic (Ntb ) at temperatures below the N phase. Anisotropic properties of MCT5 are typical of the rod-like mesogens. In particular, birefringence increases as the temperature is reduced, following the classic behaviour, described by Haller. The elastic constants also follow the standard behaviour, with their ratios being practically temperature independent. In contrast, DTC5C9 shows a dramatic departure from the standard case. Birefringence changes non-monotonously with temperature, decreasing on approaching the N–Ntb phase transition. decreases strongly to 0.4 pN near the N–Ntb transition, although remains finite. The ratios of the elastic constants in DTC5C9 show a strong temperature dependence that can be associated with the bend-induced changes in the orientational distribution function. The measured elastic properties are consistent with the tendency of the dimeric molecules to adopt bent configurations that give rise to the Ntb phase. Graphical Abstract: