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Turowski, Michal
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article
Electrorheological fluids based on modified polyacrylonitrile
Abstract
An electrorheological (ER) effect in suspensions of solid particles is related to electric polarization processes within the bulk of grains of the solid phase or/and on their surface. The nature of these processes is governed by dopants, functional groups or structure of the solid particles and the solid-liquid interface. The purpose of our investigations was to find correlations between material properties of the solid phase and the parameters of the ER effect. We focused on the role of electrical conductivity and permittivity of the dispersed phase as well as chemical nature of surface groups. As the solid phase we chose an acrylic copolymer whose properties were modified by pyrolysis in controlled conditions or by doping with a salt, and silicone oil as the liquid matrix. The prepared materials were characterized by physical and chemical methods. The impedance spectroscopy was applied to estimate the electric conductivity and permittivity of the prepared materials. The characterized powders were then dispersed in silicone oil and their flow curves in the presence of electric field were recorded. The values of yield stress of the ER fluids containing pyrolized materials ranged from 40 Pa to 300 Pa at 3kV/mm for 15% w/w concentrations of solids. The ER effect of the ionic material suspensions was strongly influenced by salt concentration in the polymer. It was also found that samples of higher electronic conductivity exhibited higher currents in comparison to other samples but not higher shear stresses. The current densities in the ionic materials suspensions were significantly lower than in the annealed samples. Pyrolized and oxidized polyacrylonitrile samples contained polar functional groups. Some of the samples were chemically treated in order to modify polarity of the functional groups and the influence of this treatment on the ER effect was studied.