Vorticity banding in rodlike virus suspensions

Area of Science:

• Colloidal science
• Soft matter physics
• Rheology

Background:

• Semiflexible colloidal rods (fd virus particles) exhibit complex behavior under shear flow.
• The paranematic-nematic biphasic region is a key area for observing unique flow-induced structures.
• Understanding shear-induced instabilities is crucial for materials science.

Purpose of the Study:

• To investigate the phenomenon of vorticity banding in fd virus particle suspensions.
• To determine the shear rate interval and conditions for uniform vorticity banding.
• To elucidate the mechanism behind banding instability and transient stability.

Main Methods:

• Experiments on suspensions of semiflexible colloidal rods (fd virus particles).
• Application of steady shear flow across the paranematic-nematic biphasic region.
• Particle tracking and polarization experiments to analyze flow dynamics.

Main Results:

• Vorticity banding observed uniformly within a specific shear rate interval (.gamma-, .gamma+).
• Shear elongation of inhomogeneities below .gamma- and heterogeneous banding above .gamma+.
• Bands exhibit a weak rolling flow superimposed on the applied shear flow.

Conclusions:

• A mechanism for vorticity banding instability is proposed, linked to normal stresses from phase separation.
• The morphology of initial inhomogeneities influences banding kinetics.
• Transient stability of banded states is explained by this mechanism.