Lehmann effect in a compensated cholesteric liquid crystal: Experimental evidence with fixed and gliding boundary conditions

Abstract : In a recent letter (Europhys. Lett. 80, 26001 (2007)), we have shown that a compensated cholesteric liquid crystal (in which the macroscopic helix completely unwinds) may be subjected to a thermomechanical torque (the so-called Lehmann effect), in agreement with previous findings of Eber and Janossy (Mol. Cryst. Liq. Cryst. Lett. 72, 233 (1982)). These results prove that one must take into account the chirality of the molecules and the absence of inversion symmetry at the macroscopic scale when deriving the constitutive equations of the phase at the compensation temperature. In this paper, we present the details of our experimental work and a new experiment performed in a sample treated for planar gliding anchoring. The latter experiment, coupled with a numerical simulation, supports the existence of a thermomechanical coupling in a compensated cholesteric.
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Submitted on : Friday, April 11, 2008 - 3:29:56 PM
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Alain Dequidt, Andrzej Zywocinski, Patrick Oswald. Lehmann effect in a compensated cholesteric liquid crystal: Experimental evidence with fixed and gliding boundary conditions. European Physical Journal E: Soft matter and biological physics, EDP Sciences: EPJ, 2008, 25 (4), pp.277-289. ⟨10.1140/epje/i2007-10290-4⟩. ⟨ensl-00272491⟩

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