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On the Origin of Vorticity Banding : experiments on fd-virus suspensions

Tumbling wagging. Binodal. 2. Spinodals. 1 2 3 4 5 6 7 8. A. Critical point. Vorticity banding. 0. 0.0. 0.5. 1.0. nem. On the Origin of Vorticity Banding : experiments on fd-virus suspensions. K. Kang, M.P. Lettinga, J. K. G. Dhont (Research Centre Juelich, Germany).

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On the Origin of Vorticity Banding : experiments on fd-virus suspensions

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  1. Tumbling wagging Binodal 2 Spinodals 1 2 3 4 5 6 7 8 A Critical point Vorticity banding 0 0.0 0.5 1.0 nem On the Origin of Vorticity Banding : experiments on fd-virus suspensions K. Kang, M.P. Lettinga, J. K. G. Dhont (Research Centre Juelich, Germany) Suspensions of very long and thin colloidal rods (fd-virus particles) exhibit vorticity banding within part of the paranematic-nematic coexistence region. Inhomogeneities that are formed after a shear-rate quench are shown to be responsible for vorticity-banding. Particle-tracking experiments reveal that there is rolling flow within the bands. This lead us to propose that vorticity banding is an elastic instability, where the shear-induced non-linear, elastic deformation of the inhomogeneities generate hoop stresses, similar to the Weissenberg effect for polymers, where now the role of polymer chains is played by the inhomogeneities [1,2,3]. Particle tracking : Fd virus : Length : 880 nm Thickness : 7 nm Persistence length : 3000nm bands are in internal rolling flow The phase diagram : 23 % : spinodal decomposition A stability analysis : flow and forces in the gradient (y-) direction z body force along the gradient direction y 35 % : nucleation and growth z y x pdf for and Growth kinetics : contains : [4,5] “Brownian contributions” +”rod-rod interactions” +“flow-structure coupling” linear bi-linear linear unstable stable stretching of inhomogeneities base density measures “the degree of inhomogeneity” band growth small ~ large growth time band width depends on the morphology Non-linear elastic deformation of the inhomogeneities gives rise to hoop stresses that lead to a banded structure of rolls non-linear elastic deformation of inhomogeneities polymer chain (Weissenberg effect) H 0 spinodal decomposition 23 % : [1] K. Kang, M.P. Lettinga, Z. Dogic, J.K.G. Dhont, Phys. Rev. E 74 (2006) 026307 [2] K. Kang, M.P. Lettinga, J.K.G. Dhont, Rheol. Acta 47 (2008) 499 [3] J.K.G. Dhont, W.J. Briels (an overview), Rheol. Acta 47 (2008) 257 [4] J.K.G. Dhont, W.J. Briels, J. Chem Phys. 117 (2002) 3992 [5] J.K.G. Dhont, W.J. Briels, J. Chem Phys. 118 (2003) 1466 35 % : nucleation and growth Inhomogeneities are at the origin of the vorticity-banding instability

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