Induced twisted-grain-boundary phases in the binary mixtures of a cholesteric and a nematic compound

Abstract

Thermodynamical, optical-texture and dielectric studies have been performed to study the phase diagram of the binary system of 5-cholesten-3β-ol-octanoate and 4-n-nonyloxybenzoic acid. It is observed that low concentrations of 5-cholesten-3β-ol-octanoate (2–30 mol %) in 4-n-nonyloxybenzoic acid induce a mean-field phase diagram derived by Renn within the framework of the chiral Chen–Lubenski model. Various optical textures of the twisted-grain-boundary (TGB) phases under different conditions of molecular anchoring have been observed. Weak transitions related to the TGB phases have been detected by temperature dependent dielectric spectroscopy.

Keywords:

• Binary mixture
• TGB phases
• Chiral Chen–Lubenski model
• Dielectric permittivity

Acknowledgements

We thank Department of Science and Technology (DST), New Delhi, for financial assistance. One of us (AKS) thanks the DST for a fellowship under a research project. We are highly grateful to Prof. S.L. Srivastava for his valuable suggestions and comments on the present work. Thanks are due to Prof. O.D. Lavrentovich, Kent State University, USA, for his valuable comments on some of our optical textures.

Notes

^aTGBA–SmC* transition; ^bCombined enthalpy for TGBA–(TGBC)–SmC* transitions.

¹In Srivastava and Dhar (1998) we were unable to resolve the temperature range of the TGBA phase, but subsequent unpublished work has shown that the temperature range of TGBA in ChM–DDOBA is ˜ 2–3°C.