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Applied Mathematics Colloquium
Friday, October 17, 11:30 am
Cullimore Lecture Hall II
New
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Bistability in Liquid Crystal Display (LCD) devices
Linda Cummings
Department of Mathematical Sciences
New Jersey Institute of Technology
Newark, NJ
Abstract
Liquid Crystal Display (LCD) devices rely on the fact that the molecules of a nematic liquid crystal have the ability to rotate the plane
of
polarized light, so that when
placed between crossed polarizers, light may pass
through the liquid crystal layer. The
amount of light
transmitted depends on the
orientation of the molecules within the layer, which in turn can be controlled
by application of an electric field.
Recently, much effort has been put into the search for bistable LCD devices, in which the director field (which
represents the local
average direction of the long axis
of the nematic liquid crystal molecules) has two
optically-distinct configurations that are both
stable in the absence of an applied
electric field. Such a device is
potentially very useful in applications such as electronic paper
(two optically-distinct states
being, of course, the minimum number required to create a meaningful display
with contrast). Once in one
of the stable configurations, the
device will maintain that configuration until disturbed from it by the
application of an
electric field. Most LCD devices currently in use rely on a
continuous power source to maintain the desired optical effect, and hence bistability
offers greatly reduced power
consumption. There are challenges to creating
a viable device however: firstly, one must design a cell that
allows for bistable
solutions, but secondly, one has to be able to switch - both ways, and quickly
- between the two configurations, by
applying an electric field. We propose one possible bistable
device that relies on the flexoelectric effect to
switch between the stable
states, and discuss its feasibility.