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Soft Matter and Biological Physics


Eur. Phys. J. E 7, 167-173 (2002)
DOI: 10.1140/epje/i20000165

A dynamic light scattering study of the viscoelastic twist mode in cholesteric liquid crystals

M.S. Giridhar and K.A. Suresh

Raman Research Institute, Bangalore 560 080, India

suresh@rri.res.in

(Received 21 November 2000 and Received in final form 4 November 2001 )

Abstract
Although viscoelastic properties of liquid crystals are very important for applications like display technology, there are not many direct techniques to study them. We have used dynamic light scattering to obtain dispersion curves for the twist mode of director fluctuations in a thermotropic cholesteric liquid crystal (cholesteric) mixture, in a wave vector range comparable to the inverse pitch of the cholesteric. In the experiment, light scattered in the vicinity of Bragg reflection is investigated using a hitherto unused scattering geometry where the scattering wave vector q is parallel to the cholesteric helix axis. By fitting the experimental data to a parabolic function of the scattering wave vector, we have determined the twist viscoelastic coefficient $k_{22}/\gamma_{1}$. We have studied the temperature dependence of $k_{22}/\gamma_{1}$ and found that the viscoelastic coefficient increases rapidly as the cholesteric-to-isotropic transition temperature is approached.

PACS
61.30.-v - Liquid crystals.
42.25.Fx - Diffraction and scattering.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002