  Magnetorheological fluids (MRF) are smart composite materials that, under an
external magnetic field, show a reversible solid-liquid transition in less than
10 ms. This study aimed to evaluate which organoclays would jellify a synthetic
oil for the formulation of MRF. Three dispersant additives for carbonyl iron
powder were evaluated. Fifteen different gelling additives from four clay
families, bentonites, hectorites, montmorillonites, and mixed mineral
thixotropes (MMT), were dispersed in oil only, keeping the same concentration,
without iron particles. The gels were then tested through amplitude and
frequency sweeps in oscillatory rheometry to evaluate their viscoelastic
behavior. All the MRFs were prepared using carbonyl iron powder HS in oil gels
with the same organoclay. All three dispersant additives showed a thixotropic
recovery above 100% in the three-interval test. Regarding the dispersibility
after one year, the MRF formulations with octan-1-amine and lecithin were
reproved, as they reached normal force peaks of 19 and 24 N, while the work was
28 and 415 mJ, respectively. The best MRF was formulated with octan-1-ol, and
resulted in a normal force of 0.33 N and 3.4 mJ at 35 mm of vane penetration.
Therefore, we conclude that the MRF with octan-1-ol and montmorillonite #6
showed a better balance between thixotropy, MR effect, and, above all, good
redispersibility.
