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Controllable alignment of nematics by nanostructured polymeric layers

Journal article
Authors Lachezar Komitov
Giovanni Barbero
Ingolf Dahl
Bertil Helgee
Nils Olsson
Published in Liquid Crystals
Volume 36
Issue 6 & 7
Pages 747-753
ISSN 0267-8292
Publication year 2009
Published at Department of Physics (GU)
Pages 747-753
Language en
Keywords titled alignment; anchoring strength; nanostructured polymers; reverse pretilt
Subject categories Material physics with surface physics, Functional materials, Surface engineering, Polymer Chemistry, Surface and colloid chemistry, Surfaces and interfaces

Abstract

A method for a continuous control of the pretilt angle of the easy axis in the range 0-90° degrees and of the anchoring strength by using nanostructured polymers as alignment layers is described. The nanostructured polymers are blends of two different side-chain polymers each of them promoting planar and homeotropic alignment, respectively. A model to interpret the alignment of a nematic liquid crystal induced by such polymer layers is proposed. We show that in this case the anisotropic part of the surface tension can be approximated by a simple extension of the Rapini-Papoular expression. The predicted trend of the pretilt of the easy axis versus the concentration of the side-chain polymer promoting the planar alignment, for instance, is in good agreement with the experimental data. We also show that the effective anchoring strength of the system depends on the concentration of the side-chain polymer promoting planar alignment, and exhibits a minimum for a well-defined value of this quantity. The results obtained in this work seems to be of importance for liquid crystal displays technology since the control of the pretilt and the anchoring strength strongly affect the performance of liquid crystal displays.

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