Date of Award

8-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Mathematical Sciences

Thesis Sponsor/Dissertation Chair/Project Chair

Philip Yecko

Committee Member

David Trubatch

Committee Member

Ashwin Vaidya

Committee Member

Eric Forgoston

Abstract

The magnetoviscous effect of applied fields on ferrofluids has been utilized in many applications in which the ferrofluid must remain in a fixed position while this effect on ferrofluids in motion has yet to be rigorously explored. In light of potential biomedical applications such as drug targeting, experiments were conducted to probe the rheology of ferrofluids on the micrometer scale. A non-conducting glass sphere of diameter 550 μm is dropped into a cylindrical container of magnetized ferrofluid of inner diameter 5.2 mm. This was repeated for two applied field strengths (980 gauss and 480 gauss) and over multiple angles with both a 4: 1 diluted ferrofluid and a 4: 1 diluted ferrofluid that had the larger particles removed (purified). Data from dilute ferrofluid show an angle-dependent in magnetized ferrofluid where maximal drag is attained when the applied field and the direction of the falling sphere are perpendicular to each other. This angle-dependence was not present in the purified ferrofluid which displayed a near-constant drag across all angles. These two results indicate that the main component of the drag experienced in the magnetized ferrofluid is due to the formation of magnetized particle threads within the ferrofluid and that large-diameter particles are responsible for this thread formation. A mathematical model was developed that formulates the drag as a fluid interaction between the array of threads within the ferrofluid and the Stokes flow due to the falling sphere. The model captures the angle-dependence seen in the experiments. The model results for falling spheres of multiple radii in a cylinder are qualitatively similar to those of uniform flow in a cylinder, implying that relative drag increases are mainly dependent upon sphere radius and negligibly affected by flow profile and wall effects.

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