Electro-optic Properties of Siloxane Based Liquid Crystal Polymers

Khalid Al-Ammar, Bahaa H.Saleh, Ali R .A.Ridha


A series of siloxane based side chain liquid crystal polymers have been prepared with a
systematic variation in spacer length. All the polymer exhibited a smectic phase, for which the
smectic-isotropic transition temperature increased as the spacer length increased. Infrared
dichroism and x-ray scattering procedures have been utilized to determine the orientational order
parameters for this series of polymers and these are related to the measured electrooptical
properties. It is found that with increasing spacer length (n) of polymer the threshold voltage is
lowered with a functional from of n-2 and that the variation of the threshold voltage arises from
changes to the intrinsic curvature elasticity rather than to differences in orientational order. A
simple model is used to indicate the origion of the effects observed which appear to arise from
the constraints offered by the coupling of the mesogenic units to the polymer backbone.

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