Catalytic Nanoshell Micromotors

Combining conventional physical vapor deposition and wet chemical etching, nanoshell catalytic motors with catalyst coated inside the shell have been fabricated. Those motors are propelled by bubble ejection or burst mechanism due to small bubble nucleation energy, and they move much faster than the Janus catalytic motors of the same size. The speeds of the motors (∼100 μm s^–1) are closely related to the bubble size and generation frequency. The experimental data show that the bubbles do not totally block the opening of the shell and, thus, achieve a fast mass transport and sustain continuous motion of the motors

Marangoni Flow Induced Collective Motion of Catalytic Micromotors

A new collective motion of non-bubble-propelled spherical Janus catalytic micromotors has been observed. When the local concentration of micromotors is high, bubbles start to form between the motors. As the bubble grows, micromotors move collectively toward the center of the bubble regardless of the orientations of their catalyst surface, eventually become aggregated, and captured around the perimeter of the bubble. It is suggested that this collective motion of the micromotors, too fast for the diffusiophoresis, can be caused by the entrainment of micromotors by the evaporation-induced Marangoni flow near the bubble. Numerical simulations confirmed that the direction and strength of such Marangoni flow are consistent with the fast, collective motion of micromotors observed experimentally

Nanostructured Scrolls from Graphene Oxide for Microjet Engines

Layered heterostructures containing graphene oxide (GO) nanosheets and 20–35 nm bimetal coatings can detach easily from a Si substrate upon sonicationspontaneously forming freestanding, micrometer-sized scrolls with GO on the outsidedue to a combination of material stresses and weak bonding between GO layers. Simple procedures can tune the scroll diameters by varying the thicknesses of the metal films, and these results are confirmed by both experiment and modeling. The selection of materials determines the stresses that control the rolling behavior, as well as the functionality of the structures. In the GO/Ti/Pt system, the Pt is located within the interior of the scrolls, which can become self-propelled microjet engines through O₂ bubbling when suspended in aqueous H₂O₂