For robots and machines to behave like soft biological organisms and be safe for contact with humans, they need to be made out of soft, lightweight, and deformable material. In particular, they require multifunctional composites that can serve as “artificial” skin, nervous tissue, and muscle. To address this, we are exploring new combinations of materials that exhibit unique combinations of electro-thermo-elastostatic properties and couplings.
Soft Matter Composites
We have recently discovered that elastomers embedded with a polydisperse suspension of liquid metal (LM) inclusions exhibit mesoscale properties never before seen in soft polymers. These LM-embedded elastomer (LMEE) composites can be tailored for either high electrical conductivity or permittivity (see above). In both cases, the electronic properties are orders of magnitude greater than those previously measured for filled elastomer composites with similar elastic properties.
M. Bartlett, A. Fassler, N. Kazem, E. Markvicka, P. Mandal, C. Majidi, “Stretchable, high-k dielectric elastomers through liquid metal inclusions,” Advanced Materials in press (2016). [link]
Reversibly Tunable Elastic Rigidity
In order for soft materials to perform mechanical work, they must be able to tune their elastic rigidity. As with natural muscle and catch connective tissue, this rigidity change must span 1-2 orders of magnitude. Recently, we have developed a novel composite material capable of changing its tensile elastic modulus between ~1 to 100 MPa, similar in range to striated muscle. This is accomplished with a percolating network of carbon black in a thermoplastic propylene-ethylene co-polymer. The composite is rigid at room temperature and softens when heated through electrical current.
W. Shan, S. Diller, A. Tutcuoglu, C. Majidi, “Rigidity-tuning conductive elastomer,” Smart Materials & Structures 24 065001 (2015). [link]
W. Shan, T. Lu, C. Majidi, “Soft-matter composites with electrically tunable elastic rigidity,” Smart Materials and Structures 22 085005 (2013). [link]
W. Shan, T. Lu, Z.H. Wang, C. Majidi, “Thermal analysis and design of a multi-layered rigidity tunable composite,” International Journal of Heat and Mass Transfer 66 271-278 (2013). [link]