Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers

Cukrov, Greta; Mosaddeghian Golestani, Youssef; Xiang, Jie; Nastishin, Yu A.; Ahmed, Z.; Welch, C.; Mehl, G. H.; Lavrentovich, Oleg D.

Abstract

We report temperature dependencies of material properties such as dielectric anisotropy, birefringence, splay (K₁₁), twist (K₂₂), and bend (K₃₃) elastic constants of the uniaxial nematic (N) phase formed by flexible dimers of DTC5C9 and compare their behavior 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 behavior, described by Haller. The elastic constants also follow the standard behavior, 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. K₃₃ 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.

Citation

Cukrov, G., Mosaddeghian Golestani, Y., Xiang, J., Nastishin, Y. A., Ahmed, Z., Welch, C., Mehl, G. H., & Lavrentovich, O. D. (2017). Comparative analysis of anisotropic material properties of uniaxial nematics formed by flexible dimers and rod-like monomers. Liquid crystals, 44(1), 219-231. https://doi.org/10.1080/02678292.2016.1240248

• Acceptance Date: Sep 20, 2016
• Online Publication Date: Oct 5, 2016
• Publication Date: 2017
• Deposit Date: Sep 28, 2016
• Publicly Available Date: Oct 5, 2016
• Journal: Liquid crystals
• Print ISSN: 0267-8292
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Volume: 44
• Issue: 1
• Pages: 219-231
• DOI: https://doi.org/10.1080/02678292.2016.1240248
• Keywords: Dimeric nematic, Elastic constants, Birefringence, Negative dielectric anisotropy, Twist-bend nematic
• Public URL: https://hull-repository.worktribe.com/output/443606
• Publisher URL: http://www.tandfonline.com/doi/full/10.1080/02678292.2016.1240248
• Additional Information: Peer Review Statement: The publishing and review policy for this title is described in its Aims & Scope.; Aim & Scope: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tlct20
• Contract Date: Sep 28, 2016