Nematic liquid crystals possess long‑range orientational order described by a director field whose distortions are mainly determined by the Frank elastic constants for splay (K₁₁), twist (K₂₂), and bend (K₃₃)1. In bent‑shaped dimers such as CB7CB, the bend elastic constant K₃₃ becomes anomalously low near the nematic twist–bend phase2, strongly influencing director configurations and electro‑optic textures. When CB7CB is mixed with the rod‑like compound 8CB, the resulting nematic phase maintains the usual orientational order while inheriting a very low3 K33 value, making the system ideal for studying elasticity‑affected textures.
This work demonstrates how such variations in elastic constants¹ shape the texture of a chiralized nematic. Usually adding a small amount of a chiral dopant to a nematic phase only induces a spontaneous twist and results in homogeneous textures. We show this is no longer the case with a reduced bend constant. Mixtures of 8CB and CB7CB were prepared and filled into planar and twisted‑nematic cells. Elastic constants K₁₁, K₂₂, and K₃₃ were then measured with changes in temperature and composition using impedance spectroscopy and electro‑optic response analysis. The texture evolution of these mixtures doped with the chiral compound S811 was observed using polarized optical microscopy. Mixtures with higher CB7CB content show a significant reduction in K₃₃, while K₁₁ and K₂₂ vary more moderately. This low‑K₃₃ regime leads to voltage‑induced striped and heliconical‑like textures, with periodicity varying with the temperature. Elastic anisotropy—particularly when K₃₃ becomes very small—plays a central role in forming and stabilizing non‑uniform nematic textures.
References: 1F. C. Frank, Discuss. Faraday Soc. 25, 19 (1958).
2I. Dozov, Europhys. Lett. 56, 247 (2001).
3A. Aouini, M. Nobili, E. Chauveau, P. Dieudonné‑George, G. Damême, D. Stoenescu, I. Dozov, and C. Blanc, Crystals 10, 1110 (2020).
