A molecular theory of smectic C liquid crystals made of rod-like molecules |
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Authors: | AS Govind NV Madhusudana |
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Institution: | (1) Raman Research Institute, C.V. Raman Avenue, Bangalore - 560 080, India, IN |
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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 U
C ∝ sin(2θ)cosφ, consistent with the biaxial nature of the phase, where θ and φ 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 α, 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.
Received 3 August 2002
RID="a"
ID="a"Present address: Department of Physics, Vijaya College, R. V. Road, Bangalore - 560 004, India.
RID="b"
ID="b"e-mail: nvmadhu@rri.res.in |
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Keywords: | PACS 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 |
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