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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Published on: October 31, 2019

Flexoelectricity and pattern formation in nematic liquid crystals.

Alexei Krekhov¹, Werner Pesch, Agnes Buka

¹Physikalisches Institut, Universität Bayreuth, Bayreuth, Germany. alexei.krekhov@uni-bayreuth.de

Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics

|July 7, 2011

Summary

We analyzed flexoelectric instability in nematic liquid crystals under alternating electric fields. Unlike static fields, dynamic fields create periodic, bursting stripe patterns (flexodomains).

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Area of Science:

Soft Matter Physics
Materials Science
Liquid Crystal Physics

Background:

Flexoelectricity describes the coupling between molecular order and electric fields in liquid crystals.
Nematic liquid crystals exhibit unique optical and electrical properties due to their anisotropic molecular alignment.
Instabilities in liquid crystals can lead to pattern formation with potential applications in displays and sensors.

Purpose of the Study:

To analyze the flexoelectric instability in a planar nematic layer subjected to an alternating electric field.
To investigate the dynamic behavior of flexodomains and their transition characteristics.
To compare flexoelectric instability with electrohydrodynamic instability in nematics.

Main Methods:

Theoretical analysis of the free energy of the nematic layer, including elastic and electric contributions.
Investigation of the system's behavior in the limit of low alternating electric field frequencies (ω→0).
Comparison of pattern formation under alternating fields versus direct current (dc) fields.

Main Results:

Alternating electric fields induce stripe patterns (flexodomains) in the nematic layer.
The low-frequency limit (ω→0) of the alternating field case is highly singular.
Unlike stationary patterns in the dc case, flexodomains appear as periodic bursts in time at small, finite frequencies.
The frequency (ω) acts as a control parameter to tune between flexodomains and convection patterns.

Conclusions:

Flexoelectric instability in nematics under alternating fields exhibits unique dynamic behavior, forming time-dependent patterns.
The frequency of the alternating electric field is crucial in determining the nature of the observed patterns.
Flexodomains represent an equilibrium transition distinct from the nonequilibrium electrohydrodynamic instability.