Yield stress of perchloric acid doped polythiophene/silicone oil suspensions

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, phi, according to a scaling law of the form, iota(y) proportional to E(alpha)phi(gamma). 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 gamma 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 degreesC, 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.