DOI: 10.1140/epje/e2003-00016-y
Switching of banana liquid crystal mesophases under field
M.F. Achard, J.Ph. Bedel, J.P. Marcerou, H.T. Nguyen and J.C. RouillonCentre de Recherches Paul Pascal (URL: http://www.crpp-bordeaux.cnrs.fr) , 115 Av. A. Schweitzer, 3360 Pessac, France marcerou@crpp.u-bordeaux.fr
(Received 18 April 2002 and Received in final form 17 January 2003 Published online: 16 April 2003 )
Abstract
Taking advantage of the great number of bent-core or "banana" compounds synthesized
and studied in the laboratory, we describe their behaviour under the application
of an external electric field. If the field were a static one, we would work within
the frame of an equilibrium phase diagram in a (field
E, temperature
T) space where
some phases would be simple dielectrics and others ferroelectric ones with a
macroscopic polarization, either spontaneous or induced by the field. In this
paper, we deal with the basic responses of "banana" liquid crystals under the
application of a low frequency (1 to 100 Hz) AC field. Firstly square-wave
voltages allow us to locate the phase boundary between dielectric (at lower field)
and ferroelectric phases (higher field) at a given temperature and field threshold.
Then we apply slowly varying AC voltages with shapes like triangle or
"triple-plateau" to check out the stability of the induced ferroelectric phase
versus field removal. Three behaviours are encountered, the unstable one (short
lifetime of the high-field ferroelectric phase) where the macroscopic polarization
is destroyed and then rebuilt in the opposite direction during each half period
and usually called "antiferroelectric"; the stable one (long lifetime) with a
polarization that rotates at constant modulus which is labeled as "ferroelectric"
and a new one where the macroscopic
polarization is proportional to the applied fied, we named this behaviour as
"superparaelectric". Let us stress that these observations apply to the
ferroelectric phases of the (
E,T) phase diagram not to the zero field (0,T)
phases observed in the usual phase characterization experiments except for an
eventual spontaneous ferroelectric phase.
61.30.-v - Liquid crystals.
61.30.Gd - Orientational order of liquid crystals; electric and magnetic field effects on order.
77.84.Nh - Liquids, emulsions, and suspensions; liquid crystals .
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003
