Direct measurement of the thermomechanical Lehmann coefficient in a compensated cholesteric liquid crystal

Abstract : The thermomechanical Lehmann coefficient \nu is directly measured as a function of temperature in a compensated cholesteric liquid crystal. The method consists of observing the continuous rotation of the director in samples treated for planar sliding anchoring when a temperature gradient is applied perpendicularly to the director. The main result is that there is no relationship between the Lehmann coefficient and the equilibrium twist $q$. In particular, we confirm that $\nu$ does not vanish at the compensation temperature at which $q=0$, in agreement with previous static measurements of Éber and Jánossy (Mol. Cryst. Liq. Cryst. {\bf 72}, (1982) 233) and of ourselves (EuroPhysics Lett. {\bf 80}, (2007) 26001). In addition, the sign of the Lehmann coefficient is determined by observing between crossed polarizers the sense of rotation of the extinction branches of the disclination lines.
Complete list of metadatas

Cited literature [5 references]  Display  Hide  Download

https://hal-ens-lyon.archives-ouvertes.fr/ensl-00351719
Contributor : Patrick Oswald <>
Submitted on : Saturday, January 10, 2009 - 5:42:01 PM
Last modification on : Monday, August 19, 2019 - 2:22:05 PM
Long-term archiving on : Tuesday, June 8, 2010 - 5:23:58 PM

File

OswDequidtEPL08.pdf
Publisher files allowed on an open archive

Identifiers

Collections

Citation

Patrick Oswald, Alain Dequidt. Direct measurement of the thermomechanical Lehmann coefficient in a compensated cholesteric liquid crystal. EPL - Europhysics Letters, European Physical Society/EDP Sciences/Società Italiana di Fisica/IOP Publishing, 2008, 83 (1), pp.16005. ⟨10.1209/0295-5075/83/16005⟩. ⟨ensl-00351719⟩

Share

Metrics

Record views

144

Files downloads

141