AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Molecular Dynamics of Evaporation and Ion Emission Process of Aqueous Nanodroplet
HIDENORI HIGASHI, Takuya Tokumi, Yasuaki Mukai, Christopher Hogan Jr., Hiroshi Suda, Mikio Kumita, Takafumi Seto, Yoshio Otani, Kanazawa University
Abstract Number: 679 Working Group: Aerosol Physics
Abstract A combination of tandem ion mobility spectrometry (IMS-IMS, with differential mobility analyzers), molecular dynamics (MD) simulations, and analytical models was adopted to investigate the process of both evaporation and ion (solvated Na+) emission from aqueous sodium chloride nanodroplets. Nanodroplets were produced via electrospray ionization (ESI) of a sodium salt solution in the experiment, while two nanodroplets were examined in MD simulations: (1) a 2,500 water molecule nanodroplet with 68 Na+ and 60 Cl- ions (an initial net charge of z = +8), and (2) a 1,000 water molecule nanodroplet with 65 Na+ and 60 Cl- ions (an initial net charge of z = +5). Specifically, we used MD simulations to examine the validity of a model for the evaporation rate incorporating both the Kelvin (surface curvature) and Thomson (electrostatic) influences, while both MD simulations and experimental measurements were compared to predictions of the ion evaporation rate equation of Labowsky et al. The excellent agreement between simulated and modeled evaporation rates for nanodroplets by a single fit parameter with solute volume fractions below 0.30. Similarly, MD simulation inferred ion emission rates are in excellent agreement with predictions based on the Labowsky et al equation. Measurements of the sizes and charge states of ESI generated NaCl clusters suggest that the charge states of these clusters are governed by ion emission, however, ion emisson appears to have occurred with lower activation energies in experiments than was anticipated based on analytical calculations as well as MD simulations.