Robust Bicontinuous Elastomer–Metal Foam Composites with Highly Tunable Stiffness

• Published in: Advanced engineering materials 2022-08, Vol.24 (8), p.n/a
• Main Authors: Sharifi, Siavash, Mohammadi Nasab, Amir, Chen, Pei-En, Liao, Yiliang, Jiao, Yang, Shan, Wanliang
• Format: Article
• Language: English
• Subjects: elastomer; LMPA foam; smart materials; soft robotics; tunable stiffness
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.202101533

Herein, a new class of robust bicontinuous elastomer–metal foam composites with highly tunable mechanical stiffness is proposed, fabricated, characterized, and demonstrated. The smart composite is a bicontinuous network of two foams, one metallic made of a low melting point alloy (LMPA) and the other elastomeric made of polydimethylsiloxane (PDMS). The stiffness of the composite can be tuned by inducing phase changes in its LMPA component. Below the melting point of the LMPA, Young's modulus of the smart composites is ≈1 GPa, whereas above the melting point of the LMPA it is ≈1 MPa. Thus, a sharp stiffness change of ≈1000× can be realized through the proposed bicontinuous foam composite structure, which is higher than all available robust smart composites. Effective medium theory is also used to predict the Young's modulus of the bicontinuous smart composites, which generates reasonable agreement with experimentally measured Young's modulus of the smart composites. Finally, the use of these smart materials as a smart joint in a robotic arm is also demonstrated. Bicontinous foam composites containing an elastomer foam and a low melting point alloy (LMPA) foam are fabricated and shown to have tunable stiffness of three orders of magnitude (≈1 GPa to ≈1 MPa) on melting of the LMPA phase. The smart composites also have shape memory effect and improved robustness, which makes them suitable actuators for soft robotics applications.