DOI: 10.1140/epje/i2002-10060-x
A molecular theory of smectic C liquid crystals made of rod-like molecules
A.S. Govind and N.V. MadhusudanaRaman Research Institute, C.V. Raman Avenue, Bangalore - 560 080, India nvmadhu@rri.res.in
(Received 3 August 2002 / Published online: 3 December 2002)
Abstract
Organic compounds exhibiting the smectic C phase are made of rod-like
molecules that have dipolar groups with lateral components. We argue that the
off-axis character of the lateral dipolar groups can account for tilt in layered
smectics (SmC, SmC*, SmI etc.). We develop a mean-field theory of the smectic C
phase based on a single-particle potential of the form
, consistent with the biaxial nature of the phase, where
and
are the polar and azimuthal angles, respectively. The hard-rod
interactions that favour the smectic A phase with zero tilt angle are also
included. The theoretical phase diagrams compare favourably with
experimental trends. Our theory also leads to the following results: i) a
first-order smectic C to smectic A transition above some value of the
McMillan parameter
, leading to a tricritical point on the smectic C to
smectic A transition line and ii) a first-order smectic C to smectic C
transition over a very small range of values of the model parameters. We
have also extended the theory to include the next higher-order term in the
tilting potential and to include the effect of different tilt angles for the
molecular core and the chain in the SmC phase.
61.30.Cz - Molecular and microscopic models and theories of liquid crystal structure.
64.70.Md - Transitions in liquid crystals.
64.60.Cn - Order-disorder transformations; statistical mechanics of model systems.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002
