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Published on: July 5, 2019
Liquid-crystal anchoring transitions on aligning substrates processed by a plasma beam
Oleg V Yaroshchuk1, Alexei D Kiselev, Ruslan M Kravchuk
1Institute of Physics of National Academy of Sciences of Ukraine, prospekt Nauki 46, 03028 Kyïv, Ukraine. olegyar@iop.kiev.ua
Summary
Plasma treatment of polyimide substrates induces anchoring transitions in nematic liquid crystals (NLCs). Increasing exposure dose causes alignment changes and easy axis reorientation, detailed by a phenomenological model.
Area of Science:
- Materials Science
- Soft Matter Physics
Background:
- Nematic liquid crystals (NLCs) exhibit unique alignment properties on surfaces.
- Polyimide substrates are widely used in liquid crystal displays.
- Surface treatment methods like plasma exposure can modify substrate properties.
Purpose of the Study:
- To investigate anchoring transitions in NLCs on plasma-treated hydrophobic polyimide substrates.
- To understand the relationship between plasma exposure dose and NLC alignment.
- To analyze the underlying mechanisms of anchoring transitions.
Main Methods:
- Fabrication of NLC cells with hydrophobic polyimide substrates.
- Plasma beam treatment of substrates with varying exposure doses.
- Optical microscopy to observe NLC alignment.
- Contact angle measurements for NLC and water.
- Analysis using a phenomenological model of competing easy axes.
Main Results:
- A continuous zenithal anchoring transition from homeotropic to tilted alignment was observed with increasing plasma dose.
- An azimuthal anchoring transition with 90-degree easy axis reorientation occurred at higher doses.
- Contact angles decreased monotonically, indicating reduced surface hydrophobicity.
- The transitions were characterized as second-order anchoring phenomena.
Conclusions:
- Plasma treatment offers a method to control NLC anchoring transitions.
- The observed transitions are governed by competing surface interactions.
- A phenomenological model successfully explains the anchoring behavior.
