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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
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Two-fluid model for the breakdown of flow alignment in nematic liquid crystals
Helmut R Brand1,2, Harald Pleiner2
1Department of Physics, University of Bayreuth, 95440 Bayreuth, Germany.
Physical Review. E
|February 19, 2021
Summary
A two-fluid model explains how flow alignment in nematic liquid crystals breaks down due to smectic clusters. A velocity difference between fluids is key to this time-dependent behavior, especially with induced smectic order.
Area of Science:
- Physics
- Materials Science
Background:
- Nematic liquid crystals exhibit flow alignment under shear.
- Smectic clusters can disrupt this alignment.
- Previous models have not fully captured this phenomenon.
Purpose of the Study:
- To present a macroscopic two-fluid model for flow alignment breakdown in nematic liquid crystals.
- To investigate the role of smectic clusters and fluid velocity differences.
Main Methods:
- Developed a macroscopic two-fluid model.
- Identified key macroscopic variables: nematic degrees of freedom, smectic cluster density, smectic order, and two velocities.
- Analyzed the model's stability and behavior under shear flow.
Main Results:
- The velocity difference between the two fluids mediates time-dependent behavior when smectic order is induced.
- A one-velocity model fails to couple induced smectic order and director orientation.
- Flow alignment breakdown becomes unstable, leading to space- and time-dependent states.
Conclusions:
- The two-fluid model successfully explains the breakdown of flow alignment in nematic liquid crystals.
- The velocity difference is crucial for describing the observed phenomena.
- The model's applicability extends beyond systems exhibiting conventional smectic phases.
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