Robust Bicontinuous Elastomer–Metal Foam Composites with Highly Tunable Stiffness

Abstract

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.

Reprogrammable allosteric metamaterials from disordered networks

“…A variety of methods have been employed to attain variable stiffness, 15 including pneumatic jamming, 16,17 magnetorheological and electrorheological materials, [18][19][20][21] shape memory polymers and alloys, [22][23][24][25] liquid crystal elastomers, [26][27][28] and phase-changing materials. [29][30][31][32][33] Typically derived from metallic alloys, waxes, or thermoplastic polymers, encapsulated phase-changing materials exhibit a decrease in modulus via the transition from solid to liquid, and raise in modulus via the reverse (solidification) transition. One phase-changing material gaining traction in the literature is Field's metal, a eutectic alloy of bismuth, indium, and tin known for its low melting point of T m = 62 1C and non-hazardous composition.…”

X-ray scattering as an effective tool for characterizing liquid metal composite morphology

“…These metals include room temperature liquids such as gallium, eutectic gallium indium (EGaIn) and Galinstan (GaInSn), as well as Field's metal that melts at 62 1C. [4][5][6][7] The gallium-based liquid metal alloys are attractive due to their low toxicity and viscosity, high thermal and electrical conductivity, and a surface oxide which rapidly forms a nanometer thick shell on droplets. 8 Liquid metal materials and their composites have enabled unprecedented combinations of high thermal conductivity, [9][10][11] electrical conductivity, 12 and selfhealing abilities in soft elastomers.…”