A new contestant in our continuous coverage of self-propelling, swimming or walking chemical entities, be it at the molecular level or the macroscopic. At long as it MOVES. See previous episode here. This week Jiuke Mu et al. treat us to graphene origami! (DOI).
Through a masking technique a strip of graphene oxide (GO) is selectively coated on one side with dopamine forming polydopamine (PDA, a melamine-like material) line patterns. This layer makes it resistant to oxidation with HI. PDA-rich regions of the strip then remain hydrophilic but the regions without PDA are reduced to hydrophobic rGO (reduced GO). When exposed to water, the PDA-rich sections tend to swell and as the PDA-poor regions do not, local bending of the strip is observed. By light exposure, water evaporates and the process is reversed. The novelty has thus far resulted in GO walkers and GO opening- and closing boxes. The more serious application the researchers are going for are artificial muscles.