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. SureshRaman 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
. We
have studied the temperature dependence of
and
found that the viscoelastic coefficient increases rapidly as the
cholesteric-to-isotropic transition temperature is approached.
61.30.-v - Liquid crystals.
42.25.Fx - Diffraction and scattering.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
