Materials scientists and engineers at the Massachusetts Institute of Technology (MIT) have developed a material that can change from one shape to another.
The morphing material works in a similar way to the process by which plants bend towards the sun to maximize the amount of light falling on their leaves. This is achieved by the intercellular (cell-to-cell) movement of fluids, causing cells on one side to swell up and become longer so that the stem bends in the other direction.
Rechargeable lithium ion batteries work in a similar way. Discharging and recharging a battery involves the movement of charged particles – lithium ions – from one side of the battery to the other and back again. This movement of ions causes the battery to expand and contract.
“I thought we could use this behaviour to another end: the actuation, or movement, of large-scale structures,” says Professor Yet-Ming Chiang, one of the MIT team leaders.
Existing “active” materials have been used to power micromotors but cannot move larger structures; the “smart” materials in piezoelectric devices, such as strain sensors and pressure gauges, convert electrical energy to mechanical energy and vice versa, but only on a microscopic scale; and shape-memory alloys require large changes in temperature to produce movement.
The new morphing material is based on the lithium ion battery but is instead made of graphite and lithium cobalt oxide, whose molecules trap moving ions, causing the material to expand by up to 19%. The material then contracts when the ions move in the opposite direction.
The material requires about 5 volts to induce morphing, far less than the hundreds of volts needed to make piezoelectric materials function. The material is also able to change shape under very high pressures, which is essential if it is to be used in aircraft wings, which are subjected to large aerodynamic forces.
This research, funded by the Defense Advanced Research Projects Agency (DARPA), has many potential applications, including military ones. It could eventually lead to morphing car parts, and aircraft wings or boat hulls which change shape according to weather conditions. Later this year, the MIT team hopes to demonstrate morphing helicopter blades that can change shape mid-spin, but it could be years or decades before this material, or something similar, is used in real aircraft.