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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.

Authors

Greta Cukrov

Youssef Mosaddeghian Golestani

Jie Xiang

Yu A. Nastishin

Z. Ahmed

C. Welch

Oleg D. Lavrentovich



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.

Publication Date 2017
Journal Liquid crystals
Print ISSN 0267-8292
Electronic ISSN 1366-5855
Publisher Taylor & Francis
Peer Reviewed Peer Reviewed
Volume 44
Issue 1
Pages 219-231
APA6 Citation Cukrov, G., Mosaddeghian Golestani, Y., Xiang, J., Nastishin, Y. A., Ahmed, Z., Welch, C., …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
DOI https://doi.org/10.1080/02678292.2016.1240248
Keywords Dimeric nematic, Elastic constants, Birefringence, Negative dielectric anisotropy, Twist-bend nematic
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....cope&journalCode=tlct20

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