Alignment of liquid crystals using Langmuir‒Blodgett films of unsymmetrical bent-core liquid crystals

The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air-water interface i...

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Bibliographic Details
Published in:Liquid crystals 2019-08, Vol.46 (10), p.1494-1504
Main Authors: Choudhary, Keerti, Gupta, R. K., Pratibha, R., Sadashiva, B. K., Manjuladevi, V.
Format: Article
Language:English
Subjects:
Alignment
Aliphatic compounds
Anchors
atomic force microscope
Brewster angle microscopy
Crystal defects
Crystals
field emission scanning electron microscope
Langmuir monolayer
Langmuir-Blodgett films
Langmuir‒-Blodgett film
Liquid crystals
Molecular chains
Molecular structure
Monomolecular films
Morphology
Mud-water interfaces
Optical properties
Substrates
Thin films
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Summary:The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air-water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir‒Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.
ISSN:0267-8292
1366-5855
DOI:10.1080/02678292.2019.1574035