Solvent-cast 4D printing and characterization of styrene-ethylene-butylene-styrene-based magnetorheological elastomeric material

Abstract

Magnetorheological elastomers (MREs), consisting of elastomers or thermoplastic elastomers (TPEs) as the soft matrix, are smart functional materials gaining attention in a wide variety of fields. TPEs offers several advantages such as easy processability and requirement of lesser additives, but their additive manufacturing using fused deposition modelling is challenging due to filament buckling and poor layer coalescence. Thus, this work presents the additive manufacturing of smart MREs consisting of spherical carbonyl iron powder (CIP) particles incorporated in styrene-ethylene-butylene-styrene (SEBS) block copolymer matrix using solvent-cast 4D (SC-4D) printing. The effect of varying filler amount on the physicomechanical and electrical characteristics of additively manufactured samples was investigated. Shore hardness and density of the MRE samples increased consistently with an increase in CIP content. However, density deviated significantly from the theoretical density beyond critical filler content (> 60 wt%). Tensile strength improved with CIP content up to 30 wt% and reduced on further increase in filler content. Elastic modulus predicted from six different theoretical models was compared with experimental results. The predictions deviated significantly from the experimental observations at higher filler contents due to complex particle–particle and particle–matrix interactions. Shrinkage and morphology analysis revealed that an increase in CIP content decreased the shrinkage and improved the shape stability of the samples. Electrical conductivity of the MRE samples was found to be close to neat SEBS sample below percolation threshold (~ 50 wt%). Beyond percolation threshold, electrical conductivity increased dramatically. Finally, the actuation capability of the flexible grippers was demonstrated in the presence of an external magnetic field.

Graphical Abstract