Evaluation of model particulate systems in electrorheological fluids.

Abstract

Electrorheology (ER) is the phenomena in which under the application of an external electric field, a reversible change in the rheological properties of a suspension takes place. ER fluids consisting of suspensions of aluminosilicate and ion exchange resin particles in mineral oil were shown to demonstrate significant ER activity. In this work aluminosilicates together with polystyrene resins were used as the model systems for studying the effect of charge carrier content and ionigenic group concentration on ER performance. Two series of aluminosilicates, zeolite A and an amorphous material, with various Si/Al ratio were synthesized. Suspensions prepared from these particulate were tested for their ER activity and dielectric properties. The ER response was enhanced as the cation content increased for zeolite A in a limited range of composition, and the crystalline materials showed stronger ER activity than the amorphous ones. The ionigenic group concentration of polystyrene resins was controlled by sulfonation reaction and the resulting degree of sulfonation varied from 48.6% to 87.5%. Electrorheological activity test showed that the ER activity increased with increasing degree of sulfonation. Dielectric measurements showed the presence of a relaxation peak for both zeolites and sulfonated polystyrene salts at low frequencies. The activation energy of this relaxation process was obtained from the fitted Arrhenius equation. For sulfonated polystyrene systems, the activation energy increased, the characteristic relaxation frequency increased, and the distribution of relaxation times broadened with increasing degree of sulfonation. This suggests that increasing the number of sulfonate-sodium ion pairs reduces the energy barrier for the displacement of the ionigenic groups but the interaction among ion pairs also increases. The dielectric behavior of sulfonated polystyrene salts under the combined high electric and shear fields was also explored.