Magnetorheology of Polydimethylsiloxane Elastomer/FeCo 3 Nanocomposite Bablu Mordina, †,‡ Rajesh Kumar Tiwari, † Dipak Kumar Setua,* ,† and Ashutosh Sharma* ,‡ † Defence Materials and Stores Research and Development Establishment, Kanpur-208013, India ‡ Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur-208016, India ABSTRACT: We investigate for the first time the magneto- rheological (MR) properties of bimetallic alloy nanocompo- sites based on cross-linked polydimethylsiloxane elastomer and ferromagnetic FeCo 3 nanoparticles. The nanoparticles (∼30 nm), with a saturation magnetization value of 166 emu/g, are synthesized by hydrazine reduction of Fe 2+ and Co 2+ metal ions. Isotropic and anisotropic nanocomposite films are prepared by a solution casting technique with 5, 10, and 20 wt % FeCo 3 in the absence and presence of 0.2 T magnetic field, respectively. The structural, morphological, and magnetic properties of nanoparticles and their composites are characterized by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, confocal and optical microscopy, and vibrating sample magnetometer analysis. Steady-state and dynamic mechanical properties of the nanocomposite under a magnetic field are evaluated by rotary shear, strain amplitude sweep, angular frequency sweep, and magnetic flux density sweep tests using a parallel plate rheometer. The effects of particle concentration, particle alignment on the magnetic properties and anisotropic coefficient of the nanocomposites are determined by measuring the hysteresis property parallel and perpendicular to the particle chain alignment. The anisotropic nanocomposites show saturation magnetization higher than that of the isotropic nanocomposites, except for the particle concentration at 20 wt %. Magnetorheological study reveals that the isotropic nanocomposites have higher absolute and relative MR effect than that of their anisotropic counterpart. Under 1.098 T magnetic field, the highest absolute MR effect of ∼21 600 Pa is found for 5 wt %, whereas the highest relative MR effect of ∼8.4% is obtained with 20 wt % isotropic composites. 1. INTRODUCTION Smart materials have physical or chemical properties which are controlled by the external stimuli such as magnetic field, stresses, electric field, temperature, moisture, pH, etc. in a reversible way. Magnetorheological elastomers (MREs) are materials with tunable rheological and viscoelastic properties under applied magnetic field, with significant applications in several emerging areas, e.g., tunable vibration absorber in mechanical devices, 1-3 actuators, 4,5 magneto-active valve for air flow control, 6 isolators in vehicle seat vibration control, 7,8 sensors, 9 rubber bushing, 10 etc. The research in the field of MREs is mainly focused on the study of the effect of different elastomer matrix; 11-15 types of magnetic particles; 4,16,17 particle size, shape, and orientation; 18,19 and surface modification of magnetic particles, 20-24 as well as the effect of addition of plasticizer 25,26 and carbon-based materials. 27-31 These studies are generally focused on determination of mechanical, viscoelastic, and magnetorheological properties of the MRE. The MREs studied in the literature are mainly based on soft magnetic microparticles, e.g., iron, cobalt, nickel, and their oxides. 11,32-34 Pure iron shows the highest saturation magnet- ization and high permeability with low remnant magnetization, which makes it a popular magnetic particle in most of the MREs. 11,14,35-43 Carbonyl iron particle is another widely explored magnetic particle in this field. 12,13,36,44-46 Magneto- rheological elastomers with hard magnetic material like BaFe 12 O 19 or SrFe 12 O 19 4,47 and Nd 2 Fe 14 B, SmCo 5 4,16 have also been reported. Giant magnetostriction of MREs containing Terfenol D as magnetostrictive particles have been reported by Wang et al. and Yin et al. 48,49 Magnetic shape memory particles (such as Ni-Mn-Ga) containing MREs have also been reported in the published literature. 50,51 However, most of above investigations have been carried out with relatively large magnetic particles of micron sizes at high loadings between 60 and 80 wt %, and even as high as 90 wt %. 52 Stepanov and co- workers studied the elastic modulus of silicone rubber composite containing different filler loading (7.1-27.6 vol %) of metallic ferrous powder (size, 2-3 μm) and magnetite (size, 0.2-0.3 μm). The study demonstrated that the shear modulus increases with higher particle content and size. 41 In another study, Stepanov et al. investigated the effect of different volume fraction (viz. 30, 37, 35 and 35) of 2-4 μm and 2-70 μm iron microparticles in the mass ratios 100:0, 50:50, 75:25, and 50:50, respectively on the magnetorheological effect of the silicon- Received: July 14, 2014 Revised: September 15, 2014 Published: October 13, 2014 Article pubs.acs.org/JPCC © 2014 American Chemical Society 25684 dx.doi.org/10.1021/jp507005s | J. Phys. Chem. C 2014, 118, 25684-25703