Molecular Dynamics Simulation Of Charged Nano-droplets Behavior In Electrospray

Electrospray Ionization-mass spectrum (ESI-MS) is an analytical technique widely used in biochemical field. The aim of ESI-MS is to extract single ions from the liquid sample and guide them into the mass spectrometer. As single ions are extracted from the nano-droplets in spray, it is valuable to investigate the behavior of the nano-droplets.Molecular dynamics is a kind of simulation method, which mainly focuses on simulating the movement of molecular systems with Newtonian mechanics. The biggest difference between molecular dynamics theory and continuity theory is that the former can be more accurate when being used to describe problems on nano-scale as it starts from the point that atoms constitute matter. As a result, Molecular dynamics simulations are well-suited to studying the ESI process, for instance, the behavior of nano-droplets in ESI.Molecular dynamics simulation method and software LAMMPS are used in this paper to investigate the behavior of the charged nano-droplet with2nm radius in different gas environment. We studied the issues including droplet morphology, cluster evaporation rate, and liquid-vapor interface. The results indicated that:(1) Metastable state of the droplet exists during the post-fission time in nitrogen atmosphere.(2) Nitrogen atmosphere accelerates the desolvation procedure, but it cannot lead to complete desolvation, so pressure-increasing, relative-molecular-mass-increasing, temperature-increasing methods are still needed.(3) Coexistence-area exists in the periphery of the droplet, in order to determine the liquid-vapor interface, we propose a value0.298exceeding which atoms with a local density are assigned to the liquid phase, and finally we get the real radius of the droplet.