What Controls the Hole Formation of Nanodroplets: Hydrodynamic or Thermodynamic Instability?

作者：Wang, Yi-Bo; Wang, Yi-Feng; Ma, Qiang; Yang, Yan-Ru; Lee, Duu-Jong; Wang, Xiao-Dong^*

来源：Langmuir : the ACS journal of surfaces and colloids , 2023, 39(33): 11760-11768.

DOI：10.1021/acs.langmuir.3c01393

• CONTACT TIME
• SPC/E WATER
• DYNAMICS

Using molecular dynamics simulations, we investigatethe air holeformation of water nanodroplets impacting hydrophilic to hydrophobicsurfaces in the range of static contact angles from 30 & DEG; to 140 & DEG;with different initial surface temperatures ranging from 300 to 1000K. We show that the hole dynamics of nanodroplets are different fromthose observed in millimeter-sized droplets. The hole formation canbe observed on smooth surfaces for nanodroplets; however, it onlyoccurs on nonsmooth surfaces for millimeter-sized droplets. We clarifythat the hole formation of nanodroplets is triggered by a nucleatedvapor bubble due to thermodynamic instability, whereas it is initiatedby air bubble entrapment during impact due to hydrodynamic instabilityfor millimeter-sized droplets. The hole formation of nanodropletsrelies heavily on the surface temperature and surface wettability,because the nucleated vapor bubble more easily occurs and grows onthe surface with high initial temperatures and hydrophobic surfaces.Based on the thermal stability analysis, a criterion is developedto predict the hole formation of nanodroplets, which verifies thedependence of hole formation on the surface temperature and wettability.Furthermore, we show that the ring-bouncing of nanodroplets is triggeredby the nucleated vapor bubble. We clarify the reasons for the reducedcontact time of nanodroplets caused by the ring-bouncing.