Magnetorheology of Single-walled Carbon Nanotube Dispersions in Mineral Oil

Abstract

The magnetorheological properties of single-walled carbon nanotube (SWNT)/mineral oil (MO) dispersions are studied using a parallel plate rheometer. Nanotubes of 1.24, 2.5, and 6.41 vol% are dispersed in mineral oil. Strain sweeps, frequency sweeps, magnetosweeps, and steady shear tests are conducted under various magnetic fields. Storage modulus G^', loss modulus G ^'', complex viscosity η*, and dynamic yield stress τ_y increase with increase in magnetic field, which is partially attributed to the increasing degree of the alignment of nanotubes in a stronger magnetic field. The alignment of nanotubes is significantly restricted at a high nanotube concentration of 6.41 vol% due to the formation of a flocculated system. Increase in magnetic field increases the elastic properties of the dispersion, decreases the viscoelastic response, and delays the non-Newtonian behavior and transition from solid to liquid state. τ_y, G^', and G^'' of SWNT/mo dispersions scale with magnetic flux density by a power law similar to magnetorheological fluids (MRFs). The shear thinning behavior of SWNT/mo dispersions follows the Ostwald-de Waele or power law. SWNT/mo of 2.5 vol% shows the largest percent increase in G^', G^'', η* among the three concentrations of dispersions during magnetosweeps.