Effect of field strength and temperature on viscoelastic properties of electrorheological suspensions of urea-modified silica particles

Temperature dependence of dynamic properties of suspensions of silica nanoparticles modified with urea during transition from liquid to quasi-solid state in the absence or presence of electric field has been investigated. In the absence of electric field the loss modulus continuously decreased, whereas the complex viscosity and storage modulus decreased steeply as a result of increasing thermal motion of suspension particles and higher fluidity of the medium. To eliminate the temperature dependence of the field-off properties in the elastic structure of the particles polarized in the electric field, the relative moduli G'/G'(0) and G ''/G ''(0) have been proposed. Thus, while the relative loss modulus at a single low frequency (1.03 rad s(-1)) was virtually independent of temperature, the growth of relative storage modulus with temperature reflects higher rigidity of the suspension structure due to increasing particle polarization, in accordance with higher permittivity and lower relaxation time obtained from dielectric measurements. (C) 2007 Elsevier B.V. All rights reserved.