Langmuir-Blodgett films as aligning layers for homeotropic alignment of liquid crystal molecules

Abstract

In this work, we studied properties of Langmuir and Langmuir-Blodgett molecular films formed by mixture of arachidic acid with nematic liquid crystal mixture having the negative dielectric anisotropy. The Langmuir films were characterised by surface pressure versus mean molecular area isotherms (π–A isotherms) and subsequently were transferred at a particular surface pressure onto hydrophillic and hydrophobic quartz substrates forming monolayer and multilayer Langmuir-Blodgett films. Miscibility of the compounds in the Langmuir films was determined. Absorption spectra of the Langmuir-Blodgett films were recorded in UV-Vis region in order to reveal organisation of the molecules. Morphology of deposited films was visualised using atomic force microscope (AFM) working in tapping mode. Finally, Langmuir-Blodgett films were deposited onto glass plates covered with indium tin oxide (ITO, transparent and conductive electrodes) and were used as aligning layers in laboratory model of Vertical Alignment-type liquid crystal display (LCD). Liquid crystal sandwich cells were filled with nematic mixture doped with a dichroic anthraquinone-dye. On the basis of the light transmission through the liquid crystal cell upon the voltage applied the basic electro-optical parameters such as threshold voltage, driving voltage and contrast were determined.

Keywords:

• liquid crystal
• negative dielectric anisotropy
• Langmuir-Blodgett film
• homeotropic alignment
• electro-optical properties

Acknowledgements

This work was supported by Research Project No N N202 482139, coordinated by National Science Centre. The authors would like to thank MSc Semir El-Ahmar for invaluable help in preparation of glass slides covered with ITO for our experiments.

JM is a scholar within Sub-measure 8.2.2 Regional Innovation Strategies, Measure 8.2 Transfer of knowledge, Priority VIII Regional human resources for the economy Human Capital Operational Program co-financed by European Social Fund and state budget.