الملخص الإنجليزي
Bi-mesogen organosiloxane molecules consist of two mesogenic moieties attached
via an alkyl chain to a short (2-5 repeat units) siloxane chain. In the smectic phase
the siloxane moieties micro-separate in to layers that act as an effective polymer
backbone. The optical properties of the material depend on the conformation of bi
mesogen molecules.
The conformation adopted by the molecules depends on a delicate balance of several
conflicting factors such as the packing in the smectic phase, the constraints at
bounding surfaces or the presence of an electric field. This work is an investigation
of the electro-optic response of a novel series of chiral bi-mesogen organosiloxane.
The material with a short (5 units) spacer between the mesogen and the siloxane
behaves as a rigid unit and responds like a smectic A material. The material with 11
units in the spacer does not respond to the electric field.
When confined in a cell treated for planar alignment the material with 10 units in the
spacer displays an unusual electro-optic response. The switching occurs in several
distinct steps. At high fields the specimen displays a progressing stripe-switching
behaviour with an increase in the response time as the field is increased reaching a
few seconds at 20 V/um. We observed a significant change in the behaviour of the
tilt angle with the temperature in treated cell, while a constant value of 34 degrees is
found in untreated cell.
Possible interpretations of the observed behaviour are presented. In the proposed
model a strong anchoring at the surface and several coexisting conformations are
involved.
