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Molecular Characterization of the Surface Excess Charge Layer in Droplets
Victor Kwan1, Styliani Consta1
1Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
Journal of the American Society for Mass Spectrometry
|June 30, 2020
Summary
The surface excess charge layer (SECL) thickness is consistent across droplet sizes and simple ion types. Macroions can extend SECL, influencing ion concentration and evaporation mechanisms.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Surface Science
Background:
- The surface excess charge layer (SECL) in droplets is crucial for distinct chemical properties.
- Understanding the influence of ion composition on SECL structure is essential.
Purpose of the Study:
- To investigate the effect of different ion types on the composition and structure of the SECL in droplets.
- To determine how ion nature and droplet size influence SECL thickness and ion distribution.
Main Methods:
- Molecular dynamics simulations were employed to model droplet systems with various ions.
- Analysis focused on SECL thickness, ion concentration profiles, and overlap with maximum ion concentration regions.
Main Results:
- SECL thickness remains invariant with droplet size and simple ion type, measuring approximately 1.5-1.7 nm.
- Macroions can increase SECL thickness to around 2.0 nm.
- Ion concentration within SECL varies with ion type and droplet size, with I⁻ and H₃O⁺ showing higher concentrations than Na⁺ and Cl⁻.
Conclusions:
- The study refines models of droplet structure by incorporating the maximum ion concentration region, which may not always coincide with SECL.
- Computed SECL ion concentrations are proposed as critical parameters for kinetic equations in ion-evaporation mechanisms.
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