Near-Infrared Light-Driven, Highly Efficient Bilayer Actuators Based on Polydopamine-Modified Reduced Graphene Oxide

Near-infrared (NIR) light-driven bilayer actuators capable of fast, highly efficient, and reversible bending/unbending motions toward periodic NIR light irradiation are fabricated by exploiting the photothermal conversion and humidity-sensitive properties of polydopamine-modified reduced graphene oxide (PDA-RGO). The bilayer actuator comprises a PDA-RGO layer prepared by a filtration method, and this layer is subsequently spin-coated with a layer of UV-cured Norland Optical Adhesive (NOA)-63. Given the hydrophilicity of PDA, the PDA-RGO layer can absorb water to swell and lose water to shrink. The intrinsic NIR absorbance of RGO sheets convertes NIR light into thermal energy, which transfers the humidity-responsive PDA-RGO layer to be NIR light-responsive. Considering that the shape of the NOA-63 layer remains unchanged under NIR light, periodic NIR light irradiation leads to asymmetric shrinkage/expansion of the bilayer, which enables fast and reversible bending/unbending motions of the bilayer actuator. We demonstrate that compared with a poly(ethylenimine)-modified graphene oxide layer, the PDA-RGO layer is unique in fabricating highly efficient bilayer actuators. A NIR light-driven walking device capable of performing quick worm-like motion on a ratchet substrate is built by connecting two polyethylene terephthalate plates as claws on opposite ends of the PDA-RGO/NOA-63 bilayer actuator.