Reactive-dynamic characteristics of a nanobubble collapse near a solid boundary using molecular dynamic simulation

Abstract

In the current research, we studied the collapse mechanism of the nanobubble under mirror and real wall protocols using molecular dynamics simulation. Moreover, we analyzed reactive properties of the real wall during the collapse process. Towards this aim, an aluminum (Al) slab has been considered as a real wall, and its behavior after the formation of a nanojet has been investigated. The obtained results indicated that the dynamics of nanobubble collapse under the mirror and real protocols are similar. The collision between the shock wave and the nanobubble leads to the collapse of nanobubble, and the nanojet was formed during this collapse process. However, the nanobubble can collapse sooner when the Al slab is used as a real wall. Moreover, the surface roughness of the Al slab during the shock propagation and nanobubble collapse was increased due to the formation of the chemical reaction between Al and water under the real wall protocol, while the mirror wall has a roughness-free surface from the beginning to the end. The chemical reaction 2Al + H2O→ AlOH + AlH creates the amorphous layer containing the AlOH and AlH species on the surface of the Al slab. This layer grows semi-smoothly during bubble shrinkage and collapse process, while the growth type was changed to an island shape after the complete collapsing. The island shape on the Al slab was formed behind the nanojet due to the water vortices that are formed after the nanobubble collapse.