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 rheological behavior of these emulsions has been investigated as a function of oil volume fraction (ϕo), oil polarity and magnetic field intensity (ψ). All the emulsions show a similar elastic response with a modulus plateau at low frequency and a small phase angle (<15°) in dynamic oscillatory shear, and shear-thinning behavior in steady shear measurements. This is independent of ϕo, oil polarity and ψ. The dynamic modulus (G′) and complex viscosity (η*) increase with an increase in ϕo 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 η* 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.