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