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Minimal model for transient swimming in a liquid crystal
Madison S Krieger1, Marcelo A Dias, Thomas R Powers
1School of Engineering, Brown University, 02912, Providence, RI, USA, madison_krieger@brown.edu.
The European Physical Journal. E, Soft Matter
|August 29, 2015
Summary
Swimming microorganisms in complex fluids take longer to reach steady speeds. This study examines startup times in liquid crystals, finding it depends on anchoring strength and fluid properties.
Area of Science:
- Fluid dynamics
- Soft matter physics
- Biophysics
Background:
- Microorganisms swim at steady speeds in simple Newtonian fluids due to rapid velocity field changes.
- In complex fluids with long relaxation times, microorganisms exhibit delayed attainment of steady-state swimming speeds.
- Understanding microorganism locomotion in complex fluids is crucial for various biological and engineering applications.
Purpose of the Study:
- To investigate the swimming startup dynamics of microorganisms in a two-dimensional hexatic liquid crystal film.
- To analyze the influence of anchoring strength and Ericksen number on the startup time.
- To determine the relationship between fluid properties (viscosities) and microorganism swimming startup.
Main Methods:
- Theoretical study of microorganism swimming startup in a 2D hexatic liquid crystal.
- Analysis of the dependence of startup time on anchoring strength and Ericksen number.
- Investigation of the role of the ratio of rotational to shear viscosity.
Main Results:
- For strong anchoring, fluid flow is immediate, but liquid crystal orientation and swimming velocity reach steady states over time proportional to relaxation time.
- High Ericksen numbers lead to behavior similar to strong anchoring, irrespective of anchoring strength.
- Startup time increases with the ratio of rotational to shear viscosity, eventually saturating.
Conclusions:
- Microorganism swimming startup in liquid crystals is significantly affected by fluid viscoelasticity and surface interactions.
- Anchoring strength and Ericksen number are key parameters governing the transition to steady-state swimming.
- The ratio of rotational to shear viscosity plays a critical role in determining the timescale of swimming startup in these complex fluids.
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