Magnetorheological behavior of Pickering emulsions stabilized by surface-modified Fe3O4 nanoparticles

Silane-modified Fe3O4 nanoparticles can stabilize emulsions of both polar and non-polar oils, and the theological behavior of these emulsions has been investigated as a function of oil volume fraction (phi(0)), oil polarity and magnetic field intensity (psi). All the emulsions show a similar elastic response with a modulus plateau at low frequency and a small phase angle (<15 degrees) in dynamic oscillatory shear, and shear-thinning behavior in steady shear measurements. This is independent of phi(0), oil polarity and psi. The dynamic modulus (G') and complex viscosity (eta*) increase with an increase in phi(0). and oil polarity, due to enhanced droplet packing and flocculation and particle aggregation on droplet surfaces. The presence of a magnetic field promotes particle attractions and associations and enhances the strength of the three-dimensional particle and droplet networks, thus remarkably increasing G' and eta* and raising the yield stress. The increase in modulus, viscosity and yield stress are beneficial for the elevation of the stability of these functional emulsions. (C) 2012 Elsevier B.V. All rights reserved.