Researchers from the University of Bordeaux have made an untethered high-energy micro-engine from shape memory nanocomposite fibres. These fibres are twisted to store mechanical energy that can then be released on demand by applying a small temperature change. The work is reported in Science.
The team, led by Jinkai Yuan and Philippe Poulin, twisted shape memory nanocomposite fibres are made from the shape-memory polymer polyvinyl alcohol (PVA) as a matrix filled with dispersed graphene oxide platelets. The graphene oxide nanosheets help to improve the torsional properties of the fibre thanks to their unique rigid 2D structures which allows them to store more mechanical energy within the fibre before they fracture.
The PVA can be programmed to adopt a certain shape – such as the highly twisted conformation demonstrated in this work – at high temperature. When heated to just above this temperature, the mechanical energy stored by the twisted fibre is rapidly released as it recovers its straight shape by untwisting.
The shape-memory nanocomposite fibres are able to deliver a record work density of around 2.8 kJ/kg and can operate for at least 10 cycles before failing. They might also potentially be coupled to elastic yarn-like cores to provide a torque that allows them to repeatedly actuate like an artificial muscle. They can fit in small spaces and reliably rotate with high speed, which means they could be used in applications such as micro-robotics, laboratories-on-a-chip, smart textiles and miniaturized medical devices.
Read the research paper: Shape memory nanocomposite fibers for untethered high-energy microengines, Jinkai Yuan et al. Science 10.1126/science.aaw3722