Flow alignment in a shearing nematic liquid crystal near a charged surface

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Polar liquid crystals (LCs) exhibit unique electro-optic properties influenced by surface interactions.
• Understanding molecular behavior near charged interfaces is crucial for advanced display and sensor technologies.
• The Ericksen-Leslie theory provides a foundational framework for describing LC dynamics.

Purpose of the Study:

• To investigate the flow alignment angle (theta(eff)(y)) and effective rotational viscosity coefficient (gamma(eff)1) of polar LCs near a charged bounding surface.
• To quantify the changes in these parameters for 4-n-octyloxy-4'-cyanobiphenyl (8OCB) under specific alignment conditions.
• To validate theoretical predictions using the Ericksen-Leslie theory.

Main Methods:

• Theoretical calculations based on the conventional Ericksen-Leslie theory.
• Analysis of the stationary flow regime for polar liquid crystals.
• Numerical computation of gamma(eff)1 and theta(eff)(y) in the vicinity of a charged surface.

Main Results:

• The flow alignment angle and effective rotational viscosity coefficient were calculated for polar LCs.
• For homeotropic alignment of 8OCB molecules on a charged indium tin oxide (ITO)-coated glass plate, gamma(eff)1 was found to increase.
• The calculated increase in gamma(eff)1 reached up to 7.8%.

Conclusions:

• Charged bounding surfaces significantly influence the effective rotational viscosity coefficient of polar liquid crystals.
• The Ericksen-Leslie theory successfully predicts these surface-induced changes in LC behavior.
• This research provides quantitative insights into LC-surface interactions relevant for device optimization.