The discovery of graphene in 2004 has ignited research into its incredible physical properties, such as superior mechanical strength and thermal conductivity. Scientists are busy exploring a wide range of possible applications, including electronics, photonics, sensors and actuators. By combining graphene with soft elastomeric materials such as PDMS, the group has created graphene/polymer composites whose responses to near-infrared (NIR) illumination depend on applied pre-strain.

Optical-to-mechanical energy conversion

At low levels of pre-strains (3–9%) the actuators showed reversible expansion while at high levels (15–40%) the actuators exhibited reversible contraction. Using these actuators, the team witnessed an extraordinary optical-to-mechanical energy conversion factor of ~7 MPa/W, three orders of magnitude greater than commercially available light driven actuating materials such as polyvinylidene fluoride (PVDF).

Compared with skeletal muscles that generate ~0.3 MPa of stress, graphene/polymer composites potentially could be fabricated in strands and assembled in such a way to bio-mimic the motion of muscle fibres.

Thin-film testing

In addition to the graphene/polymer actuators, Panchapakesan and Loomis also designed and built custom thin-film testing equipment, and remotely automated everything from pre-strain control to infrared illumination intensity and spot position inside of a robotic "black box". The apparatus was interfaced with a host computer to control test sequencing, data logging and analysis. Kinetics data revealed not only repeatable actuation and relaxation times, but also minimal sample degradation over long periods of illumination cycling.

Read more about the work in the journal Nanotechnology.