Studies on the effects of material properties structure and electrode morphology in the electrorheological response

"The electrorheological (ER) phenomenon refers to the orders of magnitude increases in the apparent viscosity and/or the development of a yield stress in suspensions of polarizable particles in a low permittivity continuous phase upon the application of large electric fields (O(1kV/mm)). In this dissertation the effects of finite conductivities were studied. Particles with conducting cores covered with an insulating layer show large yield stresses at low electric fields ($$10$\sp{-7}$ S/cm) is attributed to the existence of interfaces that control the local electric field experienced by the particles. The observed behavior cannot be explained within the framework of the existing theories. To describe the experimental results we modeled the ER fluid as a two layer dielectric. One layer has the dielectric and conducting properties of bulk polyaniline while the other is assumed to be an ""interface"". Such a model is successful in representing qualitatively the observed behavior. Another effect demonstrating the importance of interfaces is displayed in water activated ER fluids with very low water contents. While these fluids under DC conditions behave as weak ER fluids, at low AC frequencies ($<$50Hz) the particles perform an oscillatory motion following the changing polarity of the electric field and no electrode spanning structure is observed. Nevertheless, an increase in the shear stress over that of the unelectrified suspension is measured. A simple model based on convective momentum transfer due to the particle motion succeeds in representing the dependence of the excess stress on the electric field strength, shear rate and electric field frequency. Alterations in the structure result in a weak dependence on the steady state and dynamic behavior of ER fluids."

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemical and Biomolecular Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Katsikopoulos, Panagiotis Vassiliou

Contributors dc:contributor

• Zukoski, Charles F.

• Engineering, Chemical
• Chemistry, Physical
• Chemistry, Polymer

Statement dc:rights

• Copyright 1996 Katsikopoulos, Panagiotis Vassiliou

Language dc:language

eng

Identifier

9780591087994
AAI9702556
(UMI)AAI9702556

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/22439