Abstract:
We investigate the effect of shear and electric field (E) on the rheology of fumed alumina (Al2O3) − in − silicone oil suspensions (Al2O3/silicone oil) at varying Al2O3 nanoparticle loadings of 0.5 wt%–15 wt%. 0.5 wt% and 2.5 wt% Al2O3/silicone oil suspensions behave as Newtonian fluids and form gel − like suspensions at a nanoparticle loading of 10 wt% and above; attributed to the formation of a particulate network of fumed Al2O3 nanoparticles. Transient step − down experiments with 5 wt% and 15 wt% Al2O3/silicone oil suspensions indicate shear thinning and thixotropy. We also show that the dynamic rheology of gel − like 15 wt% Al2O3/silicone oil suspensions is extremely sensitive to the preshearing protocols. Depending on the preshear, partial or complete breakdown of the network structure in 15 wt% Al2O3/silicone oil suspensions is observed. Once the network structure breaks, the structural recovery doesn’t ensue at rest after the cessation of shear. On application of E, Al2O3/silicone oil suspensions with 0.5 wt%–5 wt% Al2O3 nanoparticle loading exhibit diverging low shear viscosity, frequency independent G′ along with the presence of a yield stress. The electrorheological response of 5 wt% Al2O3/silicone oil suspensions is independent of the preshearing protocols at an applied E = 1 kV/mm. Furthermore, the shear rheology with applied E does not scale with View the MathML source, instead linear and sub-linear scaling with applied E is observed.