Self-propulsion dynamics of nanosized water droplets on MoS2/graphene heterojunction surface: A molecular dynamics simulation study

Controlling the self-propelling of nanosized colloids at the heterogeneous surface is of great importance to various conventional and emerging applications. Herein, molecular dynamics simulations are performed to study the spontaneous self-propulsion dynamics of nanosized water droplets (NWDs) at the MoS2/graphene heterojunction surface, which demonstrates the propulsion of a single NWD is similar to a locomotive towing train carriage that occupies the contact area of a wetting surface robustly, thus facilitating the self-propulsion dynamics energetically and thermodynamically. The average self-propelled velocity of a single NWD can reach 5 m/s driven by the surface wettability difference. Interestingly, the propulsion of double NWDs is similar to a gluttonous snake motion, and the average velocity of the NWDs can be improved up to 6.0-9.0 m/s, which is attributed to the inter-droplet interactions derived by hydrogen bonds between the two NWDs. Besides, the diffusion of NWDs is a typical isotropic motion rather than isotropic immigration, which signifies that the self-propelled NWD can be exploited as a detecting motor or navigator in the future. Our findings provide fundamental insights into the molecular mechanism of NWD self-propulsion on a heterojunction surface, and the results could facilitate the design and fabrication of heterojunction surfaces for self-propelled NWDs