(367f) On the Existence of Flows Driven by Body Couples and Couple Stresses In Magnetic Nanoparticle Suspensions

Suspensions of magnetic nanoparticles, so-called ferrofluids, are a commercially and scientifically relevant example of fluids whose description requires consideration of the balance of internal angular momentum. For over 40 years, researchers in this field have sought to understand the mechanisms responsible for observations of flows of these fluids driven solely by the action of rotating uniform magnetic fields. One possible mechanism is that these flows are driven by the action of body couples, exerted by the magnetic field on the particle’s magnetic dipoles, and so-called couple stresses, which account for the short-range transport of internal angular momentum. However, other possible mechanisms have been advanced in the literature, such as flow driven by traveling wave magnetic field gradients or by surface phenomena, and experiments have failed to shed light on the matter due to limitations in past experimental approaches. In this talk I will briefly summarize our past theoretical and experimental work investigating this phenomenon, as well as present new experimental results using model ferrofluids consisting of suspensions of magnetic nanoparticles with thermally-blocked magnetic dipoles, for which quantitative agreement can be obtained between experiment and theoretical predictions taking into account the action of body couples and couple stresses.