| |
|
Surface
regions are crucial to the control of all liquid crystal devices,
but existing experimental techniques are unable to resolve
the depth-dependent enhanced orientational and positional
order present. The approach here will be to apply atomistic
and generic molecular simulations (using molecular data from
Prof Goodby) to relate microscopic interactions to surface-region
phase symmetry using a variety of different types of liquid
crystal molecule (drawn from the systems examined in Project
1) and substrates. This will allow a direct comparison of
phase behaviour of the simulated systems with and without
the presence of a substrate .
We will be particularly interested in developing new computer
models for substrates and determining their ability to deliver
and control novel functionality, such as bistability.
Previously, crystalline polymer surfaces
have been represented either by atomistic models, or using
appropriately parameterised corrugated potentials whereas
generic models have employed perfectly flat substrates with
azimuthally dependent coupling terms .
We will diversify the model surfaces in several ways: using
disordered or semi-crystalline polyimide and polyamide surfaces,
in which the degree of orientational order and thus the
anchoring strength will be controlled; by tethering flexible
molecules to the substrate; by representing disordered surfaces
with superpositions of corrugations, and surface roughness
through the use of longer wavelength undulations; by modellling
chemically nanopatterned surfaces to investigate the ability
of short-wavelength periodic surface coating treatments
(e.g. those based on self-assembled monolayer techniques)
to promote bistability.
In the field of ferroelectric systems,
we will explore the relationship between anchoring conditions,
and the resulting molecular organisation in smectic C* liquid
crystal phases, as a function of distance from the substrate,
in an effort to start to unravel the complex interactions
going on close to the surface in these systems. These results
will feed directly into Project 7,
and ultimately aid the prediction of the electro-optic performance
of such devices. An important issue here will be the origin
of liquid crystalline pretilt in ferroelectric systems.
Another goal here will be to provide more sophisticated
boundary conditions for continuum treatments of confined
liquid crystals, used in Projects 6,
7 and
8, than
the long standing, over-simplified, Rapini-Papoular form.
Molecular simulation is ideally suited to such a task since
the surface parameters used in continuum treatments are
really mesoscopic responses depth-averaged over an interfacial
region some 10s of nanometres thick.
Shield, M. (2002) .
McDonald, A.J. (2002)
.
Binger, D.R. and Hanna,
S. .
Binger, D.R. and Hanna,
S. .
Binger, D.R. and Hanna,
S. .
|
|
