THE TEMPERATURE-DEPENDENCE OF THE ELECTRORHEOLOGY AND RELATED ELECTRICAL-PROPERTIES OF CORN STARCH CORN-OIL SUSPENSIONS

The influence of temperature on the de electrical properties (dielectric constant and conductivity) and electrorheology (complex moduli and static post yield flow stress) of corn starch/corn oil suspensions was determined in the range 5-70 degrees C. Both electrical properties increased with temperature. The complex moduli G' and G '' determined with shear strain amplitude gamma = 0.08 and oscillation frequency f = 20 Hz decreased with temperature, whereas the quasistatic postyield stress tau(E) first increased and then decreased. The conductivity of the particles, sigma(p), and of the oil in the gap between the particles sigma(f,g) was determined from the temperature dependence of the conductivity <(sigma)over bar> of the suspensions. This gave sigma(p) much greater than sigma(f,g) for the entire temperature range considered. The measured modulus G' and the postyield flow stress tau(E) were compared with predictions of both a polarization model and a conductivity model for ER response. Although some accord existed for both models, better agreement occurred for the conductivity model. The ratio of G '' divided by the viscosity of the suspension, <(eta)over bar>, increased with temperature, indicating that the decrease in G '' with temperature was less than that of the viscosity. This was attributed to the oscillation strain being beyond that for ideal viscoelasticity. (C) 1995 Society of Rheology.