ChBE Seminar Series: Electro- and Magnetorheology
Speaker: Daniel J. Klingenberg, Professor, Dept of Chemical & Biological Engineering at the University of Wisconsin, Madison
Title: Electro- and Magnetorheology
Electrorheological (ER) and magnetorheological (MR) fluids are fascinating materials whose properties---rheological properties in particular---can be controlled by external electric and magnetic fields, respectively. Typically composed of small, polarizable or magnetizable particles dispersed in a fluid, these suspensions are notable for their enormous increase in shear viscosity when the external field is applied; viscosity increases of several orders of magnitude are common. Accompanying the rheological effects are dramatic changes in the suspension microstructure, where fibrous aggregates form in the direction of the applied field. These materials have uses in an ever-widening array of applications, some of which have reached commercialization. Automotive applications, constituting a very large potential market, include clutches and breaks, active shock absorbers and engine mounts, and a variety of other damping devices. Non-automotive applications are virtually unlimited, including robotic actuators, haptic interfaces, large deformation transducers, and biomedical devices.
This presentation will include an overview of the phenomena and underlying mechanisms of electro- and magnetorheology, along with a discussion of applications. Current research challenges will be outlined. Attention will then turn to two vignettes of research projects. In the first vignette, the enhancement of the magnetic field-induced stress in MR fluids caused by the addition of nonmagnetizable particles is described. Experimental data show that this effect is insensitive to the type of nonmagnetizable particles. Particle-level simulations are employed to show that the mechanism of enhancement is a jamming-like phenomenon, where the nonmagnetizable particles create repulsive force chains oriented along the compression axis of the shear flow. In the second vignette, electrorheological suspensions composed of nano-sized particles in oil for use in electrostatic machines are described. The challenge is to create suspensions that are stable against aggregation via van der Waals forces, and that show only weak electrorheological effects. Experiments and simulations show that sterically stabilized particles that produce stable suspensions can be engineered, and are effective for electrostatic machines.
Dan Klingenberg is a professor of Chemical and Biological Engineering at the University of Wisconsin-Madison. He received a B.S. in Chemical Engineering from the University of Missouri-Rolla in 1985, and a Ph.D. in Chemical Engineering from the University of Illinois-Urbana in 1991. He is currently the chair of the Rheology Research Center at the University of Wisconsin. His research interests include electro- and magnetorheological fluids, biomass processing, and rheology of fiber suspensions.