Thermal approaches for rigidity tunable composite design have been limited due to the relatively long activiation time. In this work, rapid and reversible changes in the mechanical rigidity of an elastic composite are accomplished with a conductive propylene-based elastomer (cPBE) embedded in an electrically and thermally insulating sheet of poly(dimethylsiloxane) (PDMS). These rigidity-tuning composites are activated by passing electrical current through the cPBE, which increases in temperature through resistive (i.e. ohmic or “Joule”) heating. Because of its relatively low Vicat softening point, only moderate current is required to rapidly heat and soften the rubber. At room temperature, the cPBE has an elastic (Young’s) modulus of 175.5 MPa and is observed to soften into a viscoplastic fluid when heated above 75 oC. Depending on the area fraction of cPBE, a composite can exhibit reversible changes in effective tensile modulus between ~0.1 and 100 MPa. Moreover, the cPBE’s unique combination of conductive, elastomeric, and thermoplastic properties eliminates the need for external Joule heating and allows for rapid activation in seconds. Lastly, we demonstrate the potential for soft robotics integration with an inflatable bending actuator that contains several cPBE-PDMS “tendon” elements. Selectively activating the tendons controls the neutral axis and direction of bending during inflation.
University of Nevada, Reno, Carnegie Mellon University
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