Inverse magnetorheological fluids Rodríguez Arco, Laura López López, Modesto Torcuato Zubarev, Andrey Gdula, Karolina García López-Durán, Juan De Dios Magnetorheological fluids Ferrofluids We report a new kind of field-responsive fluids consisting of suspensions of diamagnetic (DM) and ferromagnetic (FM) microparticles in ferrofluids. We designate them as inverse magnetorheological (IMR) fluids for analogy with inverse ferrofluids (IFFs). Observations on the particle self-assembly in IMR fluids upon magnetic field application showed that DM and FM microparticles were assembled into alternating chains oriented along the field direction. We explain such assembly on the basis of the dipolar interaction energy between particles. We also present results on the rheological properties of IMR fluids and, for comparison, of IFFs and bidispersed magnetorheological (MR) fluids. Interestingly, we found that upon magnetic field, the rheological properties of IMR fluids were enhanced with respect to bidispersed MR fluids with the same FM particle concentration, by an amount greater than the sum of the isolated contribution of DM particles. Furthermore, the field-induced yield stress was moderately increased when up to 30 % of the total FM particle content was replaced with DM particles. Beyond this point, the dependence of the yield stress on the DM content was non-monotonic, as expected for FM concentrations decreasing to zero. We explain these synergistic results by two separate phenomena: the formation of exclusion areas for FM particles due to the perturbation of the magnetic field by DM particles, and the dipole-dipole interaction between DM and FM particles, which enhances the field-induced structures. Based on this second phenomenon, we present a theoretical model for the yield stress that semi-quantitatively predicts the experimental results. 2015-11-03T09:09:54Z 2015-11-03T09:09:54Z 2014-06 journal article Rodríguez-Arco, L.; et al. Inverse magnetorheological fluids. Soft Matter, 10: 6256-6265 (2014). [http://hdl.handle.net/10481/38669] 1477-683X 1744-6848 http://hdl.handle.net/10481/38669 10.1039/c4sm01103a eng http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Royal Society of Chemistry