Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt
<p>Sodium chloride (NaCl) is one of the key components of atmospheric aerosols. The surface tension of aqueous NaCl solution (<i>σ</i><sub>NaCl, sol</sub>) and its concentration dependence are essential to determine the equilibrium water vapor pressure of aqueous NaC...
Main Authors: | , , , , , , |
---|---|
Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-12-01
|
Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/17077/2018/acp-18-17077-2018.pdf |
id |
doaj-2e6f202641634447aab6b88855d1df05 |
---|---|
record_format |
Article |
spelling |
doaj-2e6f202641634447aab6b88855d1df052020-11-25T00:30:01ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242018-12-0118170771708610.5194/acp-18-17077-2018Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten saltX. Wang0C. Chen1K. Binder2U. Kuhn3U. Pöschl4H. Su5H. Su6Y. Cheng7Y. Cheng8Max Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyMax Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyInstitut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, 55128 Mainz, GermanyMax Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyMax Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyMax Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyInstitute for Environmental and Climate Research, Jinan University, 510632 Guangzhou, ChinaMax Planck Institute for Chemistry, Multiphase Chemistry Department, Hahn-Meitner-Weg 1, 55128 Mainz, GermanyInstitute for Environmental and Climate Research, Jinan University, 510632 Guangzhou, China<p>Sodium chloride (NaCl) is one of the key components of atmospheric aerosols. The surface tension of aqueous NaCl solution (<i>σ</i><sub>NaCl, sol</sub>) 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 <i>σ</i><sub>NaCl, sol</sub> are mostly limited up to subsaturated solutions. In this study, the surface tension of aqueous NaCl is investigated by molecular dynamics (MD) simulations and the pressure tensor method from dilute to highly supersaturated solutions. We show that the linear approximation of concentration dependence of <i>σ</i><sub>NaCl, sol</sub> at molality scale can be extended to the supersaturated NaCl solution until a molality of ∼ 10.7 mol kg<sup>−1</sup> (i.e., solute mass fraction (<i>x</i><sub>NaCl</sub>) of ∼ 0.39). Energetic analyses show that this monotonic increase in surface tension is driven by the increase in excess surface enthalpy (Δ<i>H</i>) as the solution becomes concentrated. After that, the simulated <i>σ</i><sub>NaCl, sol</sub> remains almost unchanged until <i>x</i><sub>NaCl</sub> of ∼ 0.47 (near the concentration upon efflorescence). The existence of the <q>inflection point</q> at <i>x</i><sub>NaCl</sub> of ∼ 0.39 and the stable surface tension of <i>x</i><sub>NaCl</sub> between ∼ 0.39 and ∼ 0.47 can be attributed to the nearly unchanged excess surface entropy term (<i>T</i> ⋅ Δ<i>S</i>) and the excess surface enthalpy term (Δ<i>H</i>). After a <q>second inflection point</q> at <i>x</i><sub>NaCl</sub> of ∼ 0.47, the simulated <i>σ</i><sub>NaCl, sol</sub> gradually regains the growing momentum with a tendency to approach the surface tension of molten NaCl ( ∼ 175.58 mN m<sup>−1</sup> at 298.15 K, MD simulation-based extrapolation). This fast increase in <i>σ</i><sub>NaCl, sol</sub> at <i>x</i><sub>NaCl</sub> > 0.47 is a process driven by excess surface enthalpy and excess surface entropy. Our results reveal different regimes of concentration dependence of the surface tension of aqueous NaCl at 298.15 K: a water-dominated regime (<i>x</i><sub>NaCl</sub> from 0 to ∼ 0.39), a transition regime (<i>x</i><sub>NaCl</sub> from ∼ 0.39 to ∼ 0.47) and a molten NaCl-dominated regime (<i>x</i><sub>NaCl</sub> from ∼ 0.47 to 1).</p>https://www.atmos-chem-phys.net/18/17077/2018/acp-18-17077-2018.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
X. Wang C. Chen K. Binder U. Kuhn U. Pöschl H. Su H. Su Y. Cheng Y. Cheng |
spellingShingle |
X. Wang C. Chen K. Binder U. Kuhn U. Pöschl H. Su H. Su Y. Cheng Y. Cheng Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt Atmospheric Chemistry and Physics |
author_facet |
X. Wang C. Chen K. Binder U. Kuhn U. Pöschl H. Su H. Su Y. Cheng Y. Cheng |
author_sort |
X. Wang |
title |
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
title_short |
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
title_full |
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
title_fullStr |
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
title_full_unstemmed |
Molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
title_sort |
molecular dynamics simulation of the surface tension of aqueous sodium chloride: from dilute to highly supersaturated solutions and molten salt |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2018-12-01 |
description |
<p>Sodium chloride (NaCl) is one of the key components of atmospheric
aerosols. The surface tension of aqueous NaCl solution (<i>σ</i><sub>NaCl, sol</sub>)
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
<i>σ</i><sub>NaCl, sol</sub> are mostly limited up to subsaturated solutions. In this
study, the surface tension of aqueous NaCl is investigated by molecular dynamics (MD)
simulations and the pressure tensor method from dilute to highly supersaturated
solutions. We show that the linear approximation of concentration dependence of <i>σ</i><sub>NaCl, sol</sub> at molality scale can be extended to the supersaturated NaCl
solution until a molality of ∼ 10.7 mol kg<sup>−1</sup> (i.e., solute mass fraction
(<i>x</i><sub>NaCl</sub>) of ∼ 0.39). Energetic analyses show that this monotonic
increase in surface tension is driven by the increase in excess surface enthalpy (Δ<i>H</i>) as the solution becomes concentrated. After that, the simulated <i>σ</i><sub>NaCl, sol</sub> remains almost unchanged until <i>x</i><sub>NaCl</sub> of ∼ 0.47
(near the concentration upon efflorescence). The existence of the <q>inflection point</q> at
<i>x</i><sub>NaCl</sub> of ∼ 0.39 and the stable surface tension of <i>x</i><sub>NaCl</sub>
between ∼ 0.39 and ∼ 0.47 can be attributed to the nearly unchanged excess
surface entropy term (<i>T</i> ⋅ Δ<i>S</i>) and the excess surface enthalpy term (Δ<i>H</i>). After a <q>second inflection point</q> at <i>x</i><sub>NaCl</sub> of ∼ 0.47, the
simulated <i>σ</i><sub>NaCl, sol</sub> gradually regains the growing momentum with a
tendency to approach the surface tension of molten NaCl ( ∼ 175.58 mN m<sup>−1</sup>
at 298.15 K, MD simulation-based extrapolation). This fast increase in <i>σ</i><sub>NaCl, sol</sub> at <i>x</i><sub>NaCl</sub> > 0.47 is a process driven by excess surface
enthalpy and excess surface entropy. Our results reveal different regimes of
concentration dependence of the surface tension of aqueous NaCl at 298.15 K: a
water-dominated regime (<i>x</i><sub>NaCl</sub> from 0 to ∼ 0.39), a transition regime
(<i>x</i><sub>NaCl</sub> from ∼ 0.39 to ∼ 0.47) and a molten NaCl-dominated regime
(<i>x</i><sub>NaCl</sub> from ∼ 0.47 to 1).</p> |
url |
https://www.atmos-chem-phys.net/18/17077/2018/acp-18-17077-2018.pdf |
work_keys_str_mv |
AT xwang moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT cchen moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT kbinder moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT ukuhn moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT uposchl moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT hsu moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT hsu moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT ycheng moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt AT ycheng moleculardynamicssimulationofthesurfacetensionofaqueoussodiumchloridefromdilutetohighlysupersaturatedsolutionsandmoltensalt |
_version_ |
1725328370277810176 |