Magnetically Addressable Shape‐Memory and Stiffening in a Composite Elastomer

• Published in: Advanced materials (Weinheim) 2019-07, Vol.31 (29), p.e1900561-n/a
• Main Authors: Testa, Paolo, Style, Robert W., Cui, Jizhai, Donnelly, Claire, Borisova, Elena, Derlet, Peter M., Dufresne, Eric R., Heyderman, Laura J.
• Format: Article
• Language: English
• Subjects: Avionics; Deformation mechanisms; Elastomers; Embossing; liquid inclusions; magneto‐mechanical materials; magneto‐rheology; Polydimethylsiloxane; Polymer matrix composites; Rheological properties; Shape memory; Shear modulus; soft matter, X‐ray tomography; Stiffening
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201900561

With a specific stimulus, shape‐memory materials can assume a temporary shape and subsequently recover their original shape, a functionality that renders them relevant for applications in fields such as biomedicine, aerospace, and wearable electronics. Shape‐memory in polymers and composites is usually achieved by exploiting a thermal transition to program a temporary shape and subsequently recover the original shape. This may be problematic for heat‐sensitive environments, and when rapid and uniform heating is required. In this work, a soft magnetic shape‐memory composite is produced by encasing liquid droplets of magneto‐rheological fluid into a poly(dimethylsiloxane) matrix. Under the influence of a magnetic field, this material undergoes an exceptional stiffening transition, with an almost 30‐fold increase in shear modulus. Exploiting this transition, fast and fully reversible magnetic shape‐memory is demonstrated in three ways, by embossing, by simple shear, and by unconstrained 3D deformation. Using advanced synchrotron X‐ray tomography techniques, the internal structure of the material is revealed, which can be correlated with the composite stiffening and shape‐memory mechanism. This material concept, based on a simple emulsion process, can be extended to different fluids and elastomers, and can be manufactured with a wide range of methods. A soft magnetic shape‐memory composite is created by embedding droplets of magneto‐rheological fluid into a soft elastomeric matrix. When subjected to a magnetic field, the composite exhibits up to 30‐fold stiffening and displays an athermal, reversible magnetic shape‐memory, which is demonstrated with embossing, shear, and 3D deformation. Employing synchrotron X‐ray tomography, the internal structure of the material is revealed.