RESUMO
The phenomena and mechanism of electrospray modes in nanoscale are investigated from experiments and molecular dynamics simulations. It is found that the ionic concentration plays a crucial role in determining the dripping or the jetting modes in a nanoscale electrospray system. Molecular dynamics simulations uncover that the two modes are caused by the competition between the electric field stress and surface tension, which is similar to the mechanism in a macroscale electrospray system. However, in a nanoscale electrospray system, the two competing forces of the electric field stress and surface tension are more sensitive to the ion distributions than that in a macroscale electrospray system, in which the applied voltage and pressure dominate. With the decrease of the nozzle diameter to nanoscale, the ions not only affect the local electric field stress, but also destroy the hydrogen bonds among water molecules, which lead to that the ion concentration becomes a dominant factor in determining the electrospray modes in nanoscale. The discovery provides a novel method to control nanoscale electrospray modes, which may find potential applications for mass spectrometry, film deposition, and electrohydrodynamic printing.