Effective viscosity for nematic-liquid-crystal viscosity measurement using a shear horizontal wave

Area of Science:

• Materials Science
• Condensed Matter Physics
• Acoustics

Background:

• Nematic liquid crystals (NLCs) are crucial in display technologies.
• Accurate viscosity measurement is essential for understanding NLC behavior.
• Existing methods struggle with NLCs exhibiting director reorientation.

Purpose of the Study:

• To develop a quantitative method for measuring NLC effective viscosity.
• To determine NLC viscosity anisotropy using shear horizontal (SH) wave propagation.
• To explain unpredictable phase shifts observed during NLC viscosity measurements.

Main Methods:

• Utilized shear horizontal (SH) waves propagating through a glass substrate coated with NLC.
• Measured phase shifts of SH waves under applied voltages to induce director reorientation.
• Introduced and calculated an average effective viscosity incorporating director configuration and wave penetration.

Main Results:

• The proposed effective viscosity model accurately predicts measured SH wave phase shifts.
• Demonstrated quantitative analysis of NLC viscosity and anisotropy is achievable.
• Clarified the mechanism behind the unpredictable SH wave phase shifts due to director reorientation.

Conclusions:

• Effective viscosity provides a robust framework for NLC characterization using SH waves.
• This method enables precise viscosity and anisotropy measurements, crucial for NLC applications.
• The study resolves discrepancies in previous NLC viscosity measurement techniques.