Electrorheological properties of perchloric acid-doped polythiophene suspensions

Poly(3-thiopheneacetic acid), PTAA, was synthesized via an oxidative polymerization and doped with perchloric acid to control its conductivity. The rheological properties of the HClO₄-doped PTAA/silicone oil suspensions were measured in oscillatory shear to investigate the effects of electric field strength, particle concentration, and particle conductivity on electrorheological (ER) characteristics. The PTAA-based ER fluids exhibit viscoelastic behavior under an applied electric field and the ER response is amplified with increase of electric field strength. The dynamic moduli, G′ and G″, increase dramatically by ten orders of magnitude when the field strength is increased to 2 kV/mm. The suspensions exhibit a transition from fluid-like to solid-like behavior as the field strength increases, and reach a saturated ER response at a field strength of 1 kV/mm. Increase of particle concentration and particle conductivity result in a lower transition field strength. Scaling arguments are presented which successfully superpose the scaled moduli at various electric field strengths onto a single master function of the dimensionless frequency.