Resumo:
Magnetorheological Fluids (FMR) are smart materials that, when subjected to the
influence of a magnetic field, present a response in their rheological properties. This work
presents the process of preparing and characterizing a MRF containing carbonyl iron
particles dispersed in a matrix of polyalphaolefin (PAO) oil, and different types of
organoclays (OC) as a suspension stabilization element. The selection of the thixotropic
pre-gel was made in a group of 15 options prepared using different organoclays. It was
observed that phyllosilicate OC resulted in a gel with a weak viscoelastic behavior (G '~
100 to 300 Pa and G ”~ 30 to 50 Pa) in the linear viscoelastic region, while the smectite
or bentonites formed consistent viscoelastic gels (G '~ 1 to 5 kPa and G ”~ 70 to 250 Pa).
The formulation 6 (23.067 g of PAO, 1.234 g of clay, 0.436 g of polar activator) was
selected, it showed yield stress τy = (42.3 ± 2.6) Pa, storage module G '= (2690 ± 201) Pa,
cohesive energy density = 97.86 mJ / m³. Seven (A-G) stable and functional MRF were
prepared using HS / PAO iron carbonyl particles. The result of the thixotropy tests
demonstrated the values for A (147.6%), B (181.2%), C (118.3%), D (152.0%), E
(145.8%), F (140.9%) and G (114.5%) regarding thixotropic recover. The formulations
A, B and C, showed similar redispersibility results after 1 year of preparation, the normal
strength measured was up to 0.6 N. However, the fluid C showed better MR effect =
2000x , G'off = 10000 Pa, and redispersibility after one year - FN = 0.39 N and W = 9.4
mJ. The test results performed allow to the conclusion the MR fluid manufactured with
dispersant C showed a better compromise between the measured properties: G’off, τy, MR
effect, and most importantly, the redispersibility after 1 year of preparation.
