The electrorheology of suspensions consisting of Na-Fluorohectorite synthetic clay particles in silicon oil
arXiv:1002.0242 · doi:10.1122/1.3579189
Abstract
Under application of an electric field greater than a triggering electric field kV/mm, suspensions obtained by dispersing particles of the synthetic clay fluoro-hectorite in a silicon oil, aggregate into chain- and/or column-like structures parallel to the applied electric field. This micro-structuring results in a transition in the suspensions' rheological behavior, from a Newtonian-like behavior to a shear-thinning rheology with a significant yield stress. This behavior is studied as a function of particle volume fraction and strength of the applied electric field, . The steady shear flow curves are observed to scale onto a master curve with respect to , in a manner similar to what was recently found for suspensions of laponite clay [42]. In the case of Na-fluorohectorite, the corresponding dynamic yield stress is demonstrated to scale with respect to as a power law with an exponent , while the static yield stress inferred from constant shear stress tests exhibits a similar behavior with . The suspensions are also studied in the framework of thixotropic fluids: the bifurcation in the rheology behavior when letting the system flow and evolve under a constant applied shear stress is characterized, and a bifurcation yield stress, estimated as the applied shear stress at which viscosity bifurcation occurs, is measured to scale as with to 0.6. All measured yield stresses increase with the particle fraction of the suspension. For the static yield stress, a scaling law , with , is found. The results are found to be reasonably consistent with each other. Their similarities with-, and discrepancies to- results obtained on laponite-oil suspensions are discussed.