Electrorheological properties in steady shear of perchloric acid doped poly(3-thiophene acetic acid), PTAA, particles in silicone oil were investigated to determine the effects of field strength, particle concentration, doping degree (conductivity values), operating temperature, and nonionic surfactant. The PTAA/silicone oil suspensions show the typical ER response of Bingham flow behavior upon the application of electric field. The yield stress increases with electric field strength, E, and particle volume fraction, f, according to a scaling law of the form, τy∝ΕαΦγ. The scaling exponent a approaches the value of 2, predicted by the polarization model, as the particle volume fraction decreases and when the doping level of the particles decreases. The scaling exponent g tends to unity, as predicted by the polarization model, when the electric field strength is low. The yield stress under electric field initially increases with temperature up to 25 °C, and then levels off. At electric fields above of 1.5 kV/mm, the yield stress increases significantly by up to 50% on addition of small amounts of a nonionic surfactant.
Poly(3-thiophene acetic acid), PTAA, was synthesized via an oxidative polymerization and doped with perchloric acid to control its conductivity. Rheological properties of the HClO4 doped PTAA/silicone oil suspensions were measured in the oscillatory shear mode to investigate the effects of electric field strength, particle concentration, and particle conductivity on ER characteristics. The PTAA based ER fluids exhibited a viscoelastic behavior under an applied electric field and the ER response enhanced with increasing electric field strength. The dynamic moduli, G’ and G”, dramatically increased by 10 orders of magnitude when the electric field strength was increased to 2 kV/mm. Effect of particle concentration and particle conductivity were apparent at moderate electric field strengths and the suspensions show saturated ER properties at electric field strength of 1 kV/mm. Moreover, the suspensions exhibited transition from fluid-like to solid-like behavior as electric field strength increased. Higher particle concentration and higher particle conductivity induced a lower transition electric field.