Dynamics of nanoscale jet formation and impingement on flat surfaces

Molecular-dynamics simulations are used to investigate the formation of water nanojets. The fluid is forced through a nano-orifice to establish a nanojet, which then impinges on a flat surface. The simulations show that to produce jets in the 1 nm diameter range, the orifice surface must be hydrophobic, otherwise the nanojet kinetic energy/inertia may never be able to overcome the attractive forces of the surface to form a jet. In addition, for the nanojet to form a stable liquid film on the surface of impingement, the surface cannot be either hydrophobic or too hydrophilic. Finally the stability/formation of the nanojet is not sensitive to the orifice surface temperature. The same physical laws that govern flows at the micro- and macroscales adequately describe nanojet flows in the absence of strong interfacial forces.