A molecular theory of smectic C liquid crystals made of rod-like moleculesA.S. Govind and N.V. Madhusudana
Raman Research Institute, C.V. Raman Avenue, Bangalore - 560 080, India email@example.com
(Received 3 August 2002 / Published online: 3 December 2002)
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