Cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase: on the role played by the length and parity of the spacer.

Cruickshank, Ewan; Strachan, Grant J.; Thapa, Kamal; Pociecha, Damian; Salamończyk, Mirosław; Storey, John M.D.; Gorecka, Ewa; Lavrentovich, Oleg; Imrie, Corrie T.

Abstract

Six members of the 1,ω-bis(4-cyanobiphenyl-4'-yl) alkanes are reported and referred to as CBnCB in which n = 1, 15, 16, 17, 19 and 20 and indicates the number of methylene units in the spacer separating the two cyanobiphenyl units. The behaviour of CB3CB is revisited. The temperature dependence of the refractive indices, optical birefringence and dielectric permittivities measured in the nematic, N, phase for selected homologues are reported. The dimers with n ≥ 15 showed an enantiotropic N phase, and for the odd members the twist-bend nematic, NTB, phase was observed. CB3CB shows a direct NTB-isotropic, I, transition, whereas for CB1CB a virtual NTB-I transition is found. The temperature dependence of the bend elastic constant, K33, measured in the oblique helicoidal cholesteric state formed by mixtures of CBnCB with a chiral additive S811, shows strong non-monotonous behaviour with a deep minimum near the transition point to the NTB phase. The minimum value of K33 decreases as n increases. The long even members of the CBnCB series show similar values of TNI to their odd-membered counterparts, but their estimated values of TNTBN are considerably lower. This is attributed to molecular shape and its effect on K33.

Citation

CRUICKSHANK, E., STRACHAN, G.J., THAPA, K., POCIECHA, D., SALAMOŃCZYK, M., STOREY, J.M.D., GORECKA, E., LAVRENTOVICH, O. and IMRIE, C.T. 2024. Cyanobiphenyl-based liquid crystal dimers and the twist-bend nematic phase: on the role played by the length and parity of the spacer. Liquid crystals [online], 51(8-9), pages 1446-1470. Available from: https://doi.org/10.1080/02678292.2024.2381570

• Journal Article Type: Article
• Acceptance Date: Jul 12, 2024
• Online Publication Date: Aug 19, 2024
• Publication Date: Sep 30, 2024
• Deposit Date: Aug 20, 2024
• Publicly Available Date: Aug 27, 2024
• Journal: Liquid crystals
• Print ISSN: 0267-8292
• Electronic ISSN: 1366-5855
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Volume: 51
• Issue: 8-9
• Pages: 1446-1470
• DOI: https://doi.org/10.1080/02678292.2024.2381570
• Keywords: Twist-bend nematic phase; Liquid crystal dimers; Bend elastic constant; Pitch length; Spacer; Helicoidal cholesteric phase
• Public URL: https://rgu-repository.worktribe.com/output/2439507
• Additional Information: This article has been published with separate supporting information. This supporting information has been incorporated into a single file on this repository and can be found at the end of the file associated with this output.