What it is
When a complex fluid passes from laminar to transitional flow, its idealized fluid elements follow complex trajectories that give rise to secondary flows in the form of macroscopic vortices, but whether real anisotropic nanoparticles in it behave the same way was not known. The authors combined small-angle X-ray scatter microscopy with polarized light imaging, bridging seven orders of magnitude in length scale, and applied it to Taylor-Couette flow of platelet-like graphene oxide and rod-like cellulose nanocrystal suspensions. The platelets followed the macroscopic dynamics of the secondary flows, as expected at high rotational Péclet numbers, while the rods showed characteristic high-frequency orientational motion at moderate rotational Péclet numbers that correlated with the turnover frequency of the vortex instabilities.
Why it matters
The work shows markedly different multiscale dynamics underlying flow stability in the two suspensions: the platelets track the vortices of the flow, while the rods show high-frequency orientational motion that correlates with the vortex turnover. The method offers a way to connect what nanoparticles do to the stability of the macroscopic flow across scales.
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Filed underRheology and Fluid Dynamics Studies, Material Dynamics and Properties, Block Copolymer Self-Assembly