Effect of Oil-Soluble Graphene on the Tribological and Rheological Properties of Magnetorheological Fluids

Magnetorheological fluid (MRF) is a widely utilized intelligent material that faces the in-use thickening (IUT) problem caused by wear. As commonly being used polar antiwear agents aggravate the sedimentation of MRF, a new method to improve the tribological properties of MRF using nonpolar oil-soluble graphene rather than polar additives is proposed. Orthogonal and control experiments conducted with a four-ball machine show that oil-soluble graphene greatly improves the antiwear performance of MRF. More specifically, the MRF with oil-soluble graphene reduces wear volume up to about 90% compared with all control experiments, including blank samples without any additives, the samples with the surfactant but without graphene, and the ones with the commercial antiwear agent ZDDP. The results also indicate that both lubricant and MRF get the best antiwear effect when graphene concentration in the base oil is 2 mg ml(-1). This implies that oil-soluble graphene improves the tribological properties of the systems primarily by enhancing the pressure-bearing capacity of the carrier fluid. Moreover, oleophilic graphene increases the magnetorheological effect of MRF and reduces its off-state viscosity by about 4% through isolating particles and filling gaps. In summary, the proposed method can solve the IUT problem of MRF along with ensuring its performance.