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Fluids 2017, 2(4), 67;

Flow Anisotropy due to Thread-Like Nanoparticle Agglomerations in Dilute Ferrofluids

Department of Mathematical Sciences, Montclair State University, Montclair, NJ 07043, USA
National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973, USA
Physics Department, The Cooper Union, New York, NY 10003, USA
Author to whom correspondence should be addressed.
Received: 16 October 2017 / Revised: 17 November 2017 / Accepted: 1 December 2017 / Published: 7 December 2017
(This article belongs to the Special Issue Mechanics of Fluid-Particles Systems and Fluid-Solid Interactions)
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Improved knowledge of the magnetic field dependent flow properties of nanoparticle-based magnetic fluids is critical to the design of biomedical applications, including drug delivery and cell sorting. To probe the rheology of ferrofluid on a sub-millimeter scale, we examine the paths of 550 μm diameter glass spheres falling due to gravity in dilute ferrofluid, imposing a uniform magnetic field at an angle with respect to the vertical. Visualization of the spheres’ trajectories is achieved using high resolution X-ray phase-contrast imaging, allowing measurement of a terminal velocity while simultaneously revealing the formation of an array of long thread-like accumulations of magnetic nanoparticles. Drag on the sphere is largest when the applied field is normal to the path of the falling sphere, and smallest when the field and trajectory are aligned. A Stokes drag-based analysis is performed to extract an empirical tensorial viscosity from the data. We propose an approximate physical model for the observed anisotropic drag, based on the resistive force theory drag acting on a fixed non-interacting array of slender threads, aligned parallel to the magnetic field. View Full-Text
Keywords: ferrofluid; magnetoviscosity; anistotropy ferrofluid; magnetoviscosity; anistotropy

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Cali, A.; Lee, W.-K.; Trubatch, A.D.; Yecko, P. Flow Anisotropy due to Thread-Like Nanoparticle Agglomerations in Dilute Ferrofluids. Fluids 2017, 2, 67.

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