Nanoscale Jet Collision and Mixing Dynamics

Micro- and macroscale investigations have shown that colliding drops always coalesce for small values of the Weber number We = rhoU2d/sigma. Our molecular dynamic simulations show that nanojets always recoil following head-on collision even though We --> 0. The duration between collision and recoil is a function of the nanojet impact velocity Uo and the nature of intermolecular interactions. Evaporation, which promotes mixing, occurs during recoil and is enhanced by reducing intermolecular interactions. Thereafter, mixing occurs through diffusion. The mixing dynamics are independent of Uo and the orifice shape. Consistent with a continuum analysis, the characteristic nanojet diameter at stagnation ds,1 proportional to Uo, recoil time following collision tau proportional to Uo-2, and the number of evaporating molecules N proportional to Uo.