Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1013
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Molecular Dynamics Simulation of the Surface Tension of Aqueous Sodium Chloride: from Dilute to Highly Supersaturated Solutions and Molten Salt
Xiaoxiang Wang1, Chuchu Chen1, Kurt Binder2, Uwe Kuhn1, Ulrich Pöschl1, Hang Su3,1, and Yafang Cheng1,3 1Max Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, Germany
2Institut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, 55128 Mainz, Germany
3Institute for Environmental and Climate Research, Jinan University, 510632 Guangzhou, China
Abstract. Sodium chloride (NaCl) is one of the key components of atmospheric aerosols. The surface tension of aqueous NaCl solution (σNaCl,sol) and its concentration dependence are essential to determine the equilibrium water vapor pressure of aqueous NaCl droplets. Supersaturated NaCl solution droplets are observed in laboratory experiments and under atmospheric conditions, but the experimental data for σNaCl,sol are mostly limited up to sub-saturated solutions. In this study, the surface tension of aqueous NaCl is investigated by molecular dynamics (MD) simulations and pressure tensor method from dilute to highly supersaturated solutions. We show that the linear approximation of concentration dependence of σNaCl,sol at molality scale can be extended to the supersaturated NaCl solution until a molality of ~9.6 mol kg−1 (i.e., solute mass fraction (xNaCl) of ~0.36). Energetic analyses show that this monotonic increase of surface tension is driven by the increase of excessive surface enthalpy (∆H) as the solution becomes concentrated. After that, the simulated σNaCl,sol remains almost unchanged until xNaCl of ~0.47 (near the concentration upon efflorescence). The existence of the inflection point at xNaCl of ~0.36 and the stable surface tension of xNaCl between ~0.36 and ~0.47 can be attributed to a competitive growth of excessive surface entropy term (T · ∆S) and the excessive surface enthalpy term (∆H). After a second inflection point at xNaCl of ~0.47, the simulated σNaCl,sol gradually regains the growing momentum with a tendency to approach the surface tension of molten NaCl (~148.4 mN m−1 at 298.15 K, MD simulation based extrapolation). This fast increase of σNaCl,sol at xNaCl > 0.47 is primarily still an excessive surface enthalpy-driving process, although contribution from concurrent fluctuation of excessive surface entropy is expected but in a relatively smaller scale. Our results reveal different regimes of concentration dependence of the surface tension of aqueous NaCl at 298.15 K: a water-dominated regime (xNaCl from 0 to ~0.36), a transition regime (xNaCl from ~0.36 to ~0.47) and a molten NaCl-dominated regime (xNaCl from ~0.47 to 1).

Citation: Wang, X., Chen, C., Binder, K., Kuhn, U., Pöschl, U., Su, H., and Cheng, Y.: Molecular Dynamics Simulation of the Surface Tension of Aqueous Sodium Chloride: from Dilute to Highly Supersaturated Solutions and Molten Salt, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1013, in review, 2017.
Xiaoxiang Wang et al.
Xiaoxiang Wang et al.
Xiaoxiang Wang et al.

Viewed

Total article views: 169 (including HTML, PDF, and XML)

HTML PDF XML Total BibTeX EndNote
119 44 6 169 2 2

Views and downloads (calculated since 08 Nov 2017)

Cumulative views and downloads (calculated since 08 Nov 2017)

Viewed (geographical distribution)

Total article views: 169 (including HTML, PDF, and XML)

Thereof 167 with geography defined and 2 with unknown origin.

Country # Views %
  • 1

Saved

Discussed

Latest update: 19 Nov 2017
Publications Copernicus
Download
Share