Head-on collision of binary nanodroplets on rough surfaces: Impact velocity dependent spreading dynamics

HR Ren and F Yang and C Li and C Deng, APPLIED SURFACE SCIENCE, 541, 148426 (2021).

DOI: 10.1016/j.apsusc.2020.148426

The collison of binary nanodroplets on a solid surface plays a fundamental role in nanocoating and nanoprinting. However, the detailed mechanism of the collision dynamics of binary nanodroplets on rough surfaces remains undiscovered. Herein, via molecular dynamic simulations, we investigate the micromorphological evolution of the head-on collision of binary nanodroplets across a broad range of impact velocities. The impact patterns occurring over rough surfaces follow that of binary nanodroplets collision on smooth substrates (i.e., coalescence, spreading and retraction), nevertheless, the coalesced droplet experiences dramatically different deformation during the spreading phase. Concerning identical nanodroplet collisions, we present distinguished velocity regimes with various spreading dynamics: the maximum spreading factor follows a scaling law in the moderate-velocity regime, while it remains stable in the low-velocity regime. Furthermore, the maximum spreading timescale is also sensitive to the impact velocity while it is independent of the droplet size ratio. Notably, differing from the macro droplet impact, the viscosity is significant even for near-inviscid liquid droplet collision and a new scaling law is deduced to describe the spreading dynamics depending on both the Weber and Reynolds number. The present findings provide a promising approach to control the spreading behaviors of binary nanodroplet collisions which have potential applications for inkjet and spray painting.

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