Electric Field Induced Gelation of Poly(3-Thiopheneacetic Acid)/Polydi- methylsiloxane Fluids

Electrorheological (ER) properties under oscillatory shear of perchloric acid doped-poly(3-thiopheneacetic acid)/oil (P3TAA/silicone) suspensions have been investigated. The effects of electric field strength, silicone oil viscosity, and particle concentration were investigated. When the electric field strength reaches a critical value, the P3TAA-based ER fluid exhibits transitional behavior between the sol and gel states, at which point the equilibrium rheological properties satisfy the Winter-Chambon transition criteria. The critical electric field strength required for the solgel transition to occur, as determined by a frequency-independent loss tangent, decreases with increasing particle concentration. The effect of oil viscosity on the ER behavior has its greatest effect at weak electric field strength. Based on the sol-gel transition criteria, the viscoelastic scaling exponent n is found to vary between 0.83-0.98, with increasing particle concentration, corresponding to fractal dimension values between 1.61 and 1.06, respectively. The critical gel strength parameter decreases with increasing particle concentration, which correlates to the decreasing critical electric field strength.