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High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Elastic and hydrodynamic torques on a colloidal disk within a nematic liquid crystal
Joel B Rovner1, Dan S Borgnia, Daniel H Reich
1Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|December 11, 2012
Summary
Colloidal disks in liquid crystals align with the director field. Applied magnetic fields cause rotation, leading to topological transitions and defect loop shedding, revealing insights into nematic hydrodynamics.
Area of Science:
- Soft Matter Physics
- Liquid Crystal Science
Background:
- Colloidal particles in liquid crystals exhibit complex orientational behavior.
- Understanding surface anchoring and director field interactions is crucial for colloidal systems.
Purpose of the Study:
- Investigate orientation-dependent elastic energy and hydrodynamic behavior of colloidal disks.
- Analyze the response of disks to external magnetic fields and subsequent director field distortions.
- Characterize the topological transitions and defect dynamics.
Main Methods:
- Experimental observation of colloidal disks in 4-cyano-4'-pentylbiphenyl (5CB) liquid crystal.
- Application of controlled magnetic fields to induce disk rotation.
- Analysis of director field distortion and topological transitions.
- Measurement of angular relaxation dynamics.
Main Results:
- Disks align homeotropically with the director in the absence of torque.
- Elastic torque scales linearly with orientation angle (θ) up to π/2.
- A topological transition (θ→π-θ) occurs for θ>π/2, involving defect loop shedding.
- Effective drag viscosity of the nematic was extracted from relaxation measurements.
Conclusions:
- The study quantitatively validates theoretical predictions for elastic torque.
- Disk motion significantly influences the director field even at low Ericksen numbers.
- Reveals novel defect dynamics and topological transitions in colloidal liquid crystals.
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