Graphene-polydimethylsiloxane/chromium bilayer-based flexible, reversible, and large bendable photomechanical actuators

We demonstrate the fabrication of highly versatile photomechanical actuators based on graphene-polymer/metal bilayers that offers fast, low-cost fabrication, large deflection, reversible actuation under zero applied pre-strain, and wavelength-selective response. The photomechanical actuator consists of a graphene nanoplatelet (GNP)-polydimethylsiloxane (PDMS) nanocomposite with a thin chromium metal coating of 35 nm thickness on the backside of the structure. The photomechanical response of the GNP-PDMS/Cr photomechanical actuator was measured by recording the variation of the bending angle upon infrared (IR) light illumination. The bending in the bilayer actuator is caused by the generation of thermal stress due to the large mismatch (the ratio being 1/20) of the thermal expansion coefficient between the two layers as a result of IR absorption by GNPs and a subsequent increase in the local temperature. The maximum bending angle was found to be about 40 degrees with a corresponding large deflection value of about 6-7 mm within 6 s for IR illumination with an intensity of 550mWcm(-2). The corresponding actuation response and relaxation times were about 1 and 3 s, respectively. The GNP-PDMS/Cr bilayer combination when integrated with the standard surface micromachining technique of micro-electromechanical system fabrication can find useful applications in the realization of micro soft-robotics, controlled drug delivery, and light-driven micro switches i.e. micro-optomechanical systems.