Mechanical and structural investigation of isotropic and anisotropic thermoplastic magnetorheological elastomer composites based on poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS)

Abstract

Novel smart thermoplastic magnetorheological elastomer composites containing micron-sized magnetic carbonyl iron (CI) particles were prepared with a poly(styrene-ethylene-butylene-styrene) (SEBS) triblock copolymer utilized as the thermoplastic matrix rubber, and the structures and properties of the CI-SEBS composites were examined. The CI particles were uniformly dispersed in the composites prepared in the absence of the magnetic field at high temperatures T (>T$_{\rm g}^{\rm S})$, and this isotropic composite exhibited a larger storage modulus G^′ compared to the SEBS matrix at room temperature (< <T$_{\rm g}^{\rm S})$ where the EB phase therein was rubbery while the PS phase was in the glassy state. In contrast, the SEBS composite prepared under the magnetic field (with the intensity ψ < 2.5 T) at high T (>T$_{\rm g}^{\rm S})$ contained a chain structure of CI particles. This chain structure became longer and better aligned on an increase of ψ up to a saturation of the particle magnetization and on an increase of the time interval of applying the field (that allowed the particles to move and equilibrate their aligned structure). The modulus G^′ of this “pre-structured” composite measured for both cases of ψ = 0 and ψ > 0 in the direction perpendicular to the chain structure at room temperature was enhanced compared to G^′ of the isotropic composites. This difference of the filler effect (for ψ = 0) and the magnetorheological effect (for ψ > 0) between the pre-structured and isotropic composites was enhanced when the chain structure of the CI particles in the pre-structured composites became longer and better aligned. A mechanism(s) of this enhancement was discussed in relation to the morphologies (particle distribution) in the composites with the aid of a filler model and a molecular expression of the stress due to magnetically interacting particles.