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 Title: Studies on the effects of material properties structure and electrode morphology in the electrorheological response Author(s): Katsikopoulos, Panagiotis Vassiliou Doctoral Committee Chair(s): Zukoski, Charles F. Department / Program: Chemical and Biomolecular Engineering Discipline: Chemical and Biomolecular Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Physical Chemistry, Polymer Engineering, Chemical Abstract: 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. Issue Date: 1996 Type: Text Language: English URI: http://hdl.handle.net/2142/22439 ISBN: 9780591087994 Rights Information: Copyright 1996 Katsikopoulos, Panagiotis Vassiliou Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9702556 OCLC Identifier: (UMI)AAI9702556
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