Avaliação de argilas organomodificadas e dispersantes no preparo de suspensões magnetoreológicas

Abstract

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.