Nature Commun. 5, 2983 (2014)

Light-driven mechanical motors, deformable disks and actuators have been fabricated by coating 10-μm-thick disks of polycarbonate with a layer of single-walled carbon nanotubes. On exposure to light, these bilayer disks deform and curl up as a result of photothermal effects. The deformation is fast and reversible, and can produce large deflection angles. In particular, when placed directly under a solar simulator with a 1-sun intensity, the structures bent ∼90° within 0.7 s and then relaxed back to their original flat state within 0.9 s when the light is turned off. Furthermore, centimetre-scale cylindrical structures made from the bilayer can act as a motor, generating a torque that allows them to roll at a speed of 6 cm s−1 when illuminated with light from a halogen lamp. Tests indicate that such structures can survive 60,000 actuation cycles. By using carbon nanotubes with a different chirality, it is possible to tune the response wavelength of the structures. The developers from the University of California at Berkeley, Lawrence Berkeley National Laboratory and Northwestern University in the USA suggest that their structures could find applications as sun-driven motors, light-activated smart curtains and sensors.