The electrostatic polarization mechanism of the electrorheological response
Klingenberg, Daniel Joseph
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Permalink
https://hdl.handle.net/2142/19389
Description
Title
The electrostatic polarization mechanism of the electrorheological response
Author(s)
Klingenberg, Daniel Joseph
Issue Date
1991
Doctoral Committee Chair(s)
Zukoski, Charles F.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
The electrorheological (ER) response is the dramatic and reversible change in the rheological properties of a suspension due to the application of an external electric field. Many applications of this technology in stress transfer devices are possible, but development of these devices is currently limited by a lack of understanding of the fundamental mechanisms. In this dissertation, the mechanisms controlling ER response are investigated.
ER suspensions were modelled as monodisperse suspensions of hard, dielectric spheres in a Newtonian continuous phase. A molecular dynamics-like simulation technique was developed to study the behavior of this model system. Simulation of structure formation in stagnant suspensions reproduced the dominant features observed experimentally, and indicated that the response time is a sensitive function of the concentration of the disperse phase. It was shown that for concentrated suspensions and for electric field strengths $\sim$1 kV/mm, the response time is on the order of milliseconds.
Simulation of sheared ER suspensions predicted a dynamic yield stress that saturated above a critical volume fraction. This was shown to result from a transition in the suspension structure from fibers at small concentrations to dense clusters at large concentrations. Experiments performed on a model ER suspension confirmed the prediction of a plateau in the yield stress at large concentrations.
Incorporation of multipole and multibody electrostatic interactions between spheres demonstrated the sensitivity of the ER response to the dielectric properties of the phases. The ER response was also found to be sensitive to the details of the short-range repulsive forces. Optimization of these properties makes possible large values for the dynamic yield stress in ER suspensions--$\sim$1 kPa at 1 kV/mm.
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