Self-similarity in electrorheological behavior

Abstract

In this work we study the creep flow behavior of a suspension of polyaniline (PANI) particles in silicone oil under the application of an electric field. A suspension of PANI in silicone oil, a model electrorheological (ER) fluid, shows an increase in the elastic modulus and the yield stress with an increase in the magnitude of the electric field. Under the creep flow field, the application of a greater magnitude of electric field reduces the strain induced in the material while application of a greater magnitude of shear stress at any electric field enhances the strain induced in the material. Remarkably, the time evolution of strain in a PANI suspension at different stresses, electric field strengths and concentrations show superposition after appropriate shifting of the creep curves on the time and strain axes. Observed electric field–shear stress–creep time–concentration superposition demonstrates self-similarity in electrorheological behavior. We analyze the experimental data using the Bingham and Klingenberg–Zukoski models and observe that the latter predicts the experimental behavior very well. We conclude by discussing the remarkable similarities between the observed rheological behavior of ER fluids and the rheological behavior of aging soft glassy materials.