The critical velocity for nanoparticle rebound measured in a low pressure impactor

A new method of investigating the probability of adhesion of nanoparticles upon impact on a surface in a Single Stage Low Pressure Impactor is presented in this article. It allows the determination of the critical velocity for nanoparticle rebound, vcr, for the first time. First measurements with dense particles of sodium chloride and silver in the size-range between 10 nm and 100 nm are presented. Independently of the material, two regimes are identified. For particles larger than a critical size of 40 nm in case of silver and 20 nm in case of NaCl, the determined values of vcr are small, typically below 0.5 m/s, indicating low energy dissipation during collision and mainly elastic contact. For particles smaller than the respective critical size, vcr increases sharply with decreasing particle size, implying a transition to plastic deformation. The dependence of vcr on the mode of deformation is shown for structurally weakened porous NaCl particles. The values of vcr in the plastic regime are in comparable magnitude to micron-size particles.