Ion clustering in aqueous salt solutions near the liquid/vapor interface
Molecular dynamics simulations of aqueous NaCl, KCl, NaI, and KI solutions are used to study the effects of salts on the properties of the liquid/vapor interface. The simulations use the models which include both charge transfer and polarization effects. Pairing and the formation of larger ion clust...
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Інститут фізики конденсованих систем НАН України
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| Цитувати: | Ion clustering in aqueous salt solutions near the liquid/vapor interface / J.D. Smith, S.W. Rick // Condensed Matter Physics. — 2016. — Т. 19, № 2. — С. 23002: 1–10. — Бібліогр.: 69 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860018242923266048 |
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| author | Smith, J.D. Rick, S.W. |
| author_facet | Smith, J.D. Rick, S.W. |
| citation_txt | Ion clustering in aqueous salt solutions near the liquid/vapor interface / J.D. Smith, S.W. Rick // Condensed Matter Physics. — 2016. — Т. 19, № 2. — С. 23002: 1–10. — Бібліогр.: 69 назв. — англ. |
| collection | DSpace DC |
| container_title | Condensed Matter Physics |
| description | Molecular dynamics simulations of aqueous NaCl, KCl, NaI, and KI solutions are used to study the effects of salts on the properties of the liquid/vapor interface. The simulations use the models which include both charge transfer and polarization effects. Pairing and the formation of larger ion clusters occurs both in the bulk and surface region, with a decreased tendency to form larger clusters near the interface. An analysis of the roughness of the surface reveals that the chloride salts, which have less tendency to be near the surface, have a roughness that is less than pure water, while the iodide salts, which have a greater surface affinity, have a larger roughness. This suggests that ions away from the surface and ions near the surface affect the interface in opposite ways.
Моделювання методом молекулярної динамiки водних розчинiв NaCl, KCl, NaI, i KI використовується для
дослiдження ефектiв солi на властивостi границi роздiлу рiдина/пара. Симуляцiї використовують моделi,
якi включають i зарядовий перенос, i поляризацiйнi ефекти. Парування i формування бiльших iонних
кластерiв має мiсце i в об’ємi, i в поверхневiй областi з тенденцiєю до зменшення формування великих
кластерiв бiля границi роздiлу. Аналiз нерiвностi поверхнi вказує, що хлориднi солi, якi мають меншу
тенденцiю бути бiля поверхнi, мають нерiвнiсть, що є меншою, нiж у чистiй водi, тодi як йодовi солi,
якi мають бiльшу поверхневу спорiдненiсть, мають бiльшу нерiвнiсть. Це передбачає, що iони здаля вiд
поверхнi та iони поблизу поверхнi впливають на границю роздiлу протилежним чином.
|
| first_indexed | 2025-12-07T16:46:16Z |
| format | Article |
| fulltext |
Condensed Matter Physics, 2016, Vol. 19, No 2, 23002: 1–10
DOI: 10.5488/CMP.19.23002
http://www.icmp.lviv.ua/journal
Ion clustering in aqueous salt solutions
near the liquid/vapor interface
J.D. Smith, S.W. Rick
Department of Chemistry, University of New Orleans, New Orleans, LA, 70148, USA
Received November 15, 2015
Molecular dynamics simulations of aqueous NaCl, KCl, NaI, and KI solutions are used to study the effects of salts
on the properties of the liquid/vapor interface. The simulations use the models which include both charge trans-
fer and polarization effects. Pairing and the formation of larger ion clusters occurs both in the bulk and surface
region, with a decreased tendency to form larger clusters near the interface. An analysis of the roughness of the
surface reveals that the chloride salts, which have less tendency to be near the surface, have a roughness that is
less than pure water, while the iodide salts, which have a greater surface affinity, have a larger roughness. This
suggests that ions away from the surface and ions near the surface affect the interface in opposite ways.
Key words: interface, charge transfer, ion pairing, aqueous ions
PACS: 05.20.-y, 82.20.Wt, 83.10.Rs, 68.03.Hj
1. Introduction
Ions in aqueous solutions have different propensities to be near the interface with the vapor phase
[1–8]. The interest in the surface affinity follows from the relevance to the environmental properties of
the interface and from the connection to interfaces with electrodes and proteins [3, 9]. The ions which
have a greater affinity for the surface are larger, softer anions such as iodide and thiocyanate, while
smaller, harder ions (flouride or alkali cations) tend to avoid the interface. The affinity for the surface is
believed to be driven not only by size but by polarizability [1–3]. The asymmetric solvation environment
of the interface (relative to the isotropic bulk) would favor the formation of a larger induced dipole on
the ion, promoting the stability of polarizable ions at the interface. Recent studies have suggested a sepa-
rate mechanism for surface selectivity, in which the ions stabilize the surface entropically by enhancing
fluctuations of the interfacial height [8, 10, 11]. The ions with a surface affinity have a looser solvation
shell which induces interfacial fluctuations larger than either ions with tightly bound solvation shells or
the pure liquid.
Entropic stabilization of the interface through enhanced fluctuations may also promote ion pairing
at the interface [12]. Ion pairing in bulk water is suggested in a number of experimental[13–16] and
simulation [17–27] studies. Alkali halide salts show a small tendency to form pairs [22, 27–29]. At a con-
centration of 1 M, the ions pair about 10 to 20% of the time, or only slightly above a random probability
for pairing [29]. Aggregation beyond pairs are observed as well [29–36]. The clusters tend to be small,
most containing less than five ions, with a population that falls off exponentially with size [29, 34, 36].
Aqueous KI appears to be different [29]. Those ions pair with much higher probability and also form
much larger clusters. How the interface affects the clustering, beyond pairing, has not been examined.
In addition to polarization, charge transfer interactions have been shown to be important for the
properties of ion solvation [37–43] and aqueous interfaces [44–50]. Charge transfer between particles
(water-water, ion-ion, and ion-water) can lead to charged solvation shells around ions [38, 41–43, 48]
and charged interfaces [44–50]. The charge that is transferred between an ion and water is not exactly
balanced by the charge transferred with the counterion (typically, there is more charge transferred from
the anion than is transferred to the cation, [42] unless the cation is divalent [43]), resulting in a net charge
© J.D. Smith, S.W. Rick, 2016 23002-1
http://dx.doi.org/10.5488/CMP.19.23002
http://www.icmp.lviv.ua/journal
J.D. Smith, S.W. Rick
on the water molecules [29, 42, 51]. For alkali halides, each ion pair transfers about −0.1e of charge to
the water. Using the charge transfer, polarizable models, we will examine the amount of ion association
near the liquid/vapor interface for 1 molar solutions of NaCl, NaI, KCl, and KI.
2. Methods
The charge transfer model. The simulations use a recent force field which includes both charge
transfer and polarizability [29, 42, 52]. Charge transfer is treated using the discrete charge transfer (DCT)
method, in which charge is transferred between pairs based on the distance. For water, a small amount
(−0.02e) of charge is transferred from the hydrogen bond acceptor to the donor. For anions, charge is
transferred to water based on the distance between the ion center and the hydrogen on the water, and
for cations, it is based on the distance between the ion center and the oxygen atom. Charge is transferred
between unlike ions based on the distance between ion centers and no charge is transferred between ions
of the same charge. The charge transfer amounts are chosen to reproduce the results of quantum chem-
ical calculations. Polarizability is treated in the water molecules using the fluctuating charge formalism,
in which charge can redistribute among atoms on the same molecule in response to the electric field
due to other atoms, and given a charge constraint determined by the amount of charge transferred with
other particles [52]. For ions, polarizability is treated using a charge on a spring, or Drude, model [48].
The models have Lennard-Jones interactions between non-hydrogen atoms and Coulombic interactions
between charge sites.
The water-water part of the potential was optimized to reproduce a number of properties of the liq-
uid, including energy, density, pair correlation functions, dielectric constant, and diffusion constant [52].
As relates to this study, the model also accurately reproduces the surface tension [46]. The ion-water
potential was parameterized to reproduce single ion solvation free energies, coordination structure, av-
erage ion dipole and charge, in the liquid phase, plus ion-water dimer properties [42, 48]. Finally, the
ion-ion interactions were adjusted to reproduce the osmotic pressure as a function of concentration [29].
The osmotic pressure is sensitive to the amount of ion pairing and provides a good property to optimize
ion-ion interactions against [27, 28, 53–55].
Simulation details. The simulations use 2840 water molecules and 104 ions, creating a 1 M solution.
An orthorhombic box of dimensions 44×44×176 Å, periodic in all directions. This creates a water layer
about 44 Å thick, with a 132 Å thick vapor layer. Ewald sums were used for the electrostatic interactions,
with a correction to mimic a system periodic in 2 dimensions [56]. Additional details of the simulations
are the same as previously published, [29, 48] in the T V N ensemble, at 298 K, using a Nosé-Hoover
thermostat and bonds constrained using SHAKE [57]. The four different salt solutions were simulated
for a total of 6 nanoseconds. The pure liquid, with 2840 water molecules, in a 44× 44× 176 Å box was
simulated for comparison to the salt solutions.
Data analysis. The interface was characterized by fitting the water density as a function of the z-
coordinant (the direction perpendicular to the interface) to a hyperbolic tangent function,
ρ(z) = 1
2
(ρL+ρV)− 1
2
(ρL+ρV) tanh[(z − z0)/d ], (2.1)
where ρL and ρV are the liquid and vapor phase densities, respectively, z0 is the position of the Gibbsdividing surface, and d is the width. Interfacial widths are commonly reported as 10-90 thicknesses, tl ,the length over which the density changes from 90% to 10% of ρV, which is equal to 2.197d . Properties of
the interface are calculated relative to z0. Another method to define the surface uses the instantaneoussurface (INS), which accounts for the roughness of the surface [58]. This method takes a specific configu-
ration of the system and generates a density using a Gaussian convolution of the heavy atoms. A position
of the interface on a three dimensional grid can be found from the location where the density drops to
one half of its bulk value. In this analysis, the ions as well as the water molecules are used to define the
density [48, 59], and a Gaussian width of 2.4 Å and a grid spacing of 1.0 Å is used, as in previous studies
[48, 58, 59]. The INS method allows for characterization of the interface in terms of the fluctuations of
the interfacial height [8, 10, 11]. If the average height of the grid points corresponding to the INS is 〈h〉,
the fluctuations in the height can be found from 〈δh2〉 = 〈(h −〈h〉)2〉. The shape of the interface can also
23002-2
Ion clustering
be characterized by the area of the INS [12]. A useful quantity, Aexcess, is the area of the instantaneousinterface, A, divided by the area of the flat interface, or Aexcess = A/(Lx Ly ), where Lx and Ly are the boxlengths in the x and y directions. The ions are grouped into clusters based on pair distances [29]. Ions are
taken to be paired if they are within the cut-off distance, rcut, (3.5 Å for NaCl, 4.0 Å for KCl and NaI, and4.5 Å for KI) and are grouped into larger clusters if any ion is part of more than one pair [34, 36].
3. Results
Properties of the interface. The surface tension of the interface is found from the pressure tensor,
as
γ= Lz
2
[
pzz − 1
2
(pxx +py y )
]
, (3.1)
where Lz is the box length in the z-direction (perpendicular to the interface) and pαα is the diagonalelements of the pressure tensor in the α direction. Values of the surface tension are given in table 1.
For comparison, the surface tension of pure water using TIP4P-FQ+DCT model [46] is given. The 10-90
thickness, tl , is about the same for pure water, aqueous NaCl and KCl, and increases for KI and NaI. Fromthe instantaneous interface analysis, the fluctuations in the interfacial height, 〈δh2〉1/2, and the excess
surface area, Aexcess can be determined. The results show that for the NaCl and KCl solutions, 〈δh2〉1/2
and Aexcess are less than they are for pure water and for the NaI and KI solutions, 〈δh2〉1/2 and Aexcess areabout equal to the pure water values. The 10-90 thickness, tl , is about the same for pure water, aqueousNaCl and KCl, and increases for KI and NaI. This would be consistent with more iodide than chloride ions
at the surface.
Table 1. Surface tension, interfacial width, fluctuations in interface height, and excess surface area for
water and the four 1 M solutions.
γ tl 〈δh2〉1/2 Aexcess(dyn/cm) (Å) (Å)
pure water 73±1 4.01±0.07 1.19±0.02 1.152±0.001
NaCl 89±2 4.05±0.05 1.16±0.01 1.148±0.001
KCl 87±1 4.01±0.06 1.17±0.02 1.149±0.001
NaI 76±2 4.33±0.11 1.21±0.02 1.152±0.001
KI 78±2 4.72±0.14 1.23±0.02 1.154±0.001
Ion densities. The ion densities relative to the Gibbs dividing surface are shown in figure 1. Iodide
shows more surface affinity that chloride, and the cations occupy positions beneath away from the sur-
face. Figure 2 shows the density profiles relative to the instantaneous interface. When viewed this way,
the density profiles are sharper and the water density shows some structure [48, 59, 66]. The anions and
cations are seen to be in distinct layers relative to the instantaneous interface.
Ion pairing. The distribution of ion pairs is shown in figure 3. Shown is the distribution of pairs,
based on the center of mass of the pair, divided by the total number of the pairs in the whole system.
Enhanced pairing at the interface is apparent for all salts, as is especially evident from the distribution
relative to the instantaneous surface. Pairing with iodide is enhanced more than chloride, as might be
expected since iodide has a greater surface affinity. The increased amount of pairing may arise since
there are more anions at the surface or because there are properties of the surface that promote pairing,
as suggested by Venkateshwaran, et al. [12].
Ion clustering. To analyze how clustering changes at the surface, the system is split up into three
regions, as suggested by figures 2 and 3. The z-coordinate of the center of the cluster relative to the
instantaneous surface, zcluster, is used. The first region (zcluster < 5 Å) corresponds to the surface, the
second (5 Å < zcluster < 12 Å), the subsurface region, and the third (zcluster > 12 Å) corresponds to the
bulk region. Within each region, cluster distributions, p(n), are determined. As done previously, [29] the
23002-3
J.D. Smith, S.W. Rick
Figure 1. (Color online) Density profiles as a function of the distance from the Gibbs dividing surface for
the anion (green dashed line), cation (red dotted line) and water (blue solid line). Values less than zero
correspond the the vapor phase. The densities for the ions have been multiplied by a factor of 100 to be
on the same scale as the water densities.
distributions are normalized as
Nion∑
n=1
p(n)n = 1 (3.2)
so that p(1) = 1 if all ions are present as single ions, p(2) = 1/2 if all are present as pairs, and p(n) = 1/n
Figure 2. (Color online) Density profiles as a function of the distance from the instantaneous surface for
the anion (green dashed line), cation (red dotted line) and water (blue solid line). Values less than zero
correspond the the vapor phase. The densities for the ions have been multiplied by a factor of 100 to be
on the same scale as the water densities.
23002-4
Ion clustering
0
0.02
0.04
0.06
0.08
0.1
0 10 20
(B) KCl
0
0.02
0.04
0.06
0.08
0.1
pa
ir
de
ns
ity
0 10 20
(A) NaCl
0
0.1
0.2
0.3
0 10 20
z (Å)
(D) KI
0
0.1
0.2
0.3
pa
ir
de
ns
ity
0 10 20
z (Å)
(C) NaI
Figure 3. (Color online) Pair probability as a function of the distance from the Gibbs dividing surface (red
solid line) and instantaneous surface (blue dashed line).
if all ions are in a n-particle cluster. The distributions are shown in figure 4, comparing the surface to
the bulk region. Larger clusters are seen with KI, consistent with the earlier study on bulk solutions [29].
There are differences between the bulk and the surface region, with less larger clusters at the surface.
On the scale of the plot, differences for small clusters are hard to discern, so the p(n) values are given
in table 2. KCl and NaI show more, while NaCl shows slightly less and KI significantly less pairing at the
surface.
Charge transfer effects. The charge of the ions and the water molecules are shown in figure 5. The
charge transfer to the ions is less at the interface and both the anions and the cations have charges
closer to their full charge. The cations show a bigger change at the interface. For the dilute ions, the
DCT models show that the charge of the anions decreases at the interface, as the ions lose solvation shell
10−6
10−5
10−4
10−3
10−2
10−1
100
2 4 6 8 10
(B) KCl
10−6
10−5
10−4
10−3
10−2
10−1
100
p(
n)
2 4 6 8 10
(A) NaCl
10−6
10−5
10−4
10−3
10−2
10−1
100
4 8 12 16 20
n
(D) KI
10−6
10−5
10−4
10−3
10−2
10−1
100
p(
n)
1 2 3 4 5
n
(C) NaI
Figure 4. (Color online) Distribution of clusters near the surface (red solid line) and the bulk (blue dashed
line) regions.
23002-5
J.D. Smith, S.W. Rick
Table 2. Distributions of clusters of size one to three in the three different regions relative to the interface.
p(1) p(2) p(3)
NaCl surface 0.87±0.02 0.060±0.009 0.003±0.001
subsurface 0.85±0.01 0.064±0.003 0.007±0.001
bulk 0.84±0.01 0.068±0.005 0.007±0.002
KCl surface 0.80±0.02 0.089±0.008 0.006±0.001
subsurface 0.81±0.01 0.078±0.004 0.008±0.001
bulk 0.82±0.01 0.076±0.004 0.008±0.001
NaI surface 0.89±0.02 0.053±0.008 0.002±0.001
subsurface 0.93±0.01 0.031±0.002 0.002±0.001
bulk 0.92±0.02 0.037±0.007 0.002±0.001
KI surface 0.71±0.01 0.086±0.003 0.020±0.002
subsurface 0.65±0.02 0.089±0.005 0.023±0.003
bulk 0.49±0.02 0.163±0.002 0.032±0.002
water molecules, while for cations, the charge is relatively unchanged [48]. Pairing decreases the charge
of the anion and increases the charge of the cation, as demonstrated with the DCT models [29], ab initio
analysis of NaCl structures from classical simulations [51], and ab initio molecular dynamics studies of
LiF in water [68]. Pairing leads to a less charge transfer, from the DCT perspective, because there is less
charge transfer between an ion pair than there is between an ion and water, particulariy for the anions.
At the surface, both an increased pairing and a loss of some of the solvation shell, for anions, leads to a
less charge transfer.
In the bulk, the charge of the anions is around −0.8e and the cations is 0.9e , leading to an overall
charge of the water molecules. This arrises because more charge is transferred to the water from chlo-
0.9
0.95
0 10 20
Na
K
ca
tio
n
ch
ar
ge
(e
)
-0.85
-0.8
0 10 20
Cl
an
io
n
ch
ar
ge
(e
)
I
-0.004
-0.002
0
w
at
er
ch
ar
ge
(e
)
0 10 20
z (Å)
Figure 5. (Color online) Charge of the cation (top), anion (middle) and water molecules (bottom) as a
function of distance from the Gibbs dividing surface for NaCl (green dashed line), KCl (black solid line),
NaI (blue dot-dashed line), and KI (red dotted line).
23002-6
Ion clustering
ride or iodide than is transferred from sodium or potassium. At a 1 M concentration, there is about 55
water molecules for every ion pair, so the charge imbalance of −0.1e gets among 55 water molecules,
giving each an average charge of about −0.002e. This charge on the water molecules, also seen in other
simulation studies, [29, 42, 51] has implications on the dynamics of the water [69]. At the surface, the
water molecules can acquire a charge due to hydrogen bond imbalances [44–50]. Molecules right at the
surface tend to accept more hydrogen bonds than they donate to other molecules (often termed “dan-
gling hydrogen bonds”) while molecules right beneath the surface donate more than they accept. This
gives rise to water molecules which are more negative near the surface (around z = 2 Å) and molecules
in the next layer (around z = 6 Å) that are more positive than bulk waters.
4. Conclusion
The simulation results find that the surface tension depends most strongly on the anion, with a
smaller surface tension for iodide. This is in agreement with experiment, which finds that the surface
tension increases as KI ≈ NaI < KCl < NaCl [60]. The increases are larger for the model, over 10 dyn/cm
for NaCl for example, than they are experimentally (1.64 dyn/cm). The surface tension for pure water
varies by over 30 dyn/cm for different water models [46, 61, 62], so surface tension is very sensitive to
the details of the intermolecular interactions. Simulations using non-polarizable models have found good
agreement for the surface tension for aqueous NaCl [63–65], while the results using polarizable models
are not as good, showing a decrease in the surface tension [65]. We are encouraged that the DCT models
give the correct trend.
As in previous studies, with DCT models at dilute concentrations [48] and other polarizable potentials
[7], the iodide and chloride ions both show an affinity for the surface, with the iodide ion showing more
than chloride (figure 1). In dilute solutions, sodium and potassium are repelled from the surface [48].
In the 1 M solutions, the presence of the anion at the surface leads to a peak in the cation distribution
beneath the surface, so that there is an interfacial region that is neutral. This peak is slightly enhanced in
the KI solution. The ion peaks become more narrow and higher and the water density has the structure,
when they are plotted relative to the instantaneous interface (figure 2), consistent with the previous
studies [48, 59, 66], the ion peaks become more narrow and higher and the water density shows some
structure. From this analysis, it is apparent that the chloride ion surface peak matches the water surface
peak while the iodide peak is shifted towards the vapor phase. The sodium and potassium peaks are
shifted more into the liquid phase than they appear in figure 1. In either analysis of the density, there is
a region of depleted anion density beneath the surface, consistent with other studies [64, 67]. For dilute
anions, there is no such region [48], indicating that this feature is induced by the presence of the other
ions.
The four solutions all showmore pairing at the surface (figure 3). The amount of pairing is a combina-
tion of an increased density of anions and the tendency to pair. That is, theremight bemore pairs because
there are more ions or because the surface promotes pairing, as has been proposed by Venkateshwaran
et al. [12]. The fraction for each ion to have no other ions in its solvation shell, making it a cluster of size
one, is greater for NaCl and KI, and slightly less for KCl and NaI (table 2). Relative to the amount of ions
present, there is less pairing for NaCl and KI. For all four ion solutions, there are fewer larger clusters at
the surface than in the bulk region (figure 4). The tendency to form larger clusters is the greatest for KI,
as reported earlier for the bulk [29]. For these solutions, there does not seem to be an enhanced tendency
to form pairs, or larger clusters, at the surface, possibly reflecting the differences between dilute and
concentrated solutions.
The shape of the interface can be characterized by the fluctuations in the interfacial height, 〈δh2〉1/2,
and the instantaneous surface area, as in previous studies [8, 10–12]. Here, we define the excess surface
area, Aexcess, as the instantaneous surface area divided by the surface area of the flat interface. Boththese properties are measures of the deviations from a flat interface, 〈δh2〉1/2 would be zero and Aexcesswould be one for a perfectly flat interface. They both increase as the surface gets rougher. For NaCl and
KCl, the surface is flatter than the pure solution (see table 1). A decrease in the surface area and in the
surface height fluctuations is consistent with a large increase in the surface tension of these two salts.
For iodide salts, the surface is rougher than the chloride salts, and 〈δh2〉1/2 and Aexcess are equal to the
23002-7
J.D. Smith, S.W. Rick
values for pure water. Simulation studies on dilute ions suggest that a single ion [8, 10, 11] or an ion
pair [12] enhance surface fluctuations. Combining those results with those of this study suggests that ions
in the bulk decrease the fluctuations, and increase the surface tension, and ions at the interface increase
fluctuations, and decrease the surface tension.
5. Acknowledgements
This work was supported by the National Science Foundation under contract number CHE-0611679.
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J.D. Smith, S.W. Rick
Iонне кластерування у водному розчинi солi
поблизу границi роздiлу рiдина/пара
Ж.Д. Смiт, С.В. Рiк
Хiмiчний факультет, Унiверситет Нью Орлеану, Нью Орлеан, Луiзiана 70148, США
Моделювання методом молекулярної динамiки водних розчинiв NaCl, KCl, NaI, i KI використовується для
дослiдження ефектiв солi на властивостi границi роздiлу рiдина/пара. Симуляцiї використовують моделi,
якi включають i зарядовий перенос, i поляризацiйнi ефекти. Парування i формування бiльших iонних
кластерiв має мiсце i в об’ємi, i в поверхневiй областi з тенденцiєю до зменшення формування великих
кластерiв бiля границi роздiлу. Аналiз нерiвностi поверхнi вказує, що хлориднi солi, якi мають меншу
тенденцiю бути бiля поверхнi, мають нерiвнiсть, що є меншою, нiж у чистiй водi, тодi як йодовi солi,
якi мають бiльшу поверхневу спорiдненiсть, мають бiльшу нерiвнiсть. Це передбачає, що iони здаля вiд
поверхнi та iони поблизу поверхнi впливають на границю роздiлу протилежним чином.
Ключовi слова: границя роздiлу, перенос заряду, парування iонiв, воднi iони
23002-10
Introduction
Methods
Results
Conclusion
Acknowledgements
|
| id | nasplib_isofts_kiev_ua-123456789-155802 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1607-324X |
| language | English |
| last_indexed | 2025-12-07T16:46:16Z |
| publishDate | 2016 |
| publisher | Інститут фізики конденсованих систем НАН України |
| record_format | dspace |
| spelling | Smith, J.D. Rick, S.W. 2019-06-17T12:53:21Z 2019-06-17T12:53:21Z 2016 Ion clustering in aqueous salt solutions near the liquid/vapor interface / J.D. Smith, S.W. Rick // Condensed Matter Physics. — 2016. — Т. 19, № 2. — С. 23002: 1–10. — Бібліогр.: 69 назв. — англ. 1607-324X DOI:10.5488/CMP.19.23002 arXiv:1603.07106 PACS: 05.20.-y, 82.20.Wt, 83.10.Rs, 68.03.Hj https://nasplib.isofts.kiev.ua/handle/123456789/155802 Molecular dynamics simulations of aqueous NaCl, KCl, NaI, and KI solutions are used to study the effects of salts on the properties of the liquid/vapor interface. The simulations use the models which include both charge transfer and polarization effects. Pairing and the formation of larger ion clusters occurs both in the bulk and surface region, with a decreased tendency to form larger clusters near the interface. An analysis of the roughness of the surface reveals that the chloride salts, which have less tendency to be near the surface, have a roughness that is less than pure water, while the iodide salts, which have a greater surface affinity, have a larger roughness. This suggests that ions away from the surface and ions near the surface affect the interface in opposite ways. Моделювання методом молекулярної динамiки водних розчинiв NaCl, KCl, NaI, i KI використовується для
 дослiдження ефектiв солi на властивостi границi роздiлу рiдина/пара. Симуляцiї використовують моделi,
 якi включають i зарядовий перенос, i поляризацiйнi ефекти. Парування i формування бiльших iонних
 кластерiв має мiсце i в об’ємi, i в поверхневiй областi з тенденцiєю до зменшення формування великих
 кластерiв бiля границi роздiлу. Аналiз нерiвностi поверхнi вказує, що хлориднi солi, якi мають меншу
 тенденцiю бути бiля поверхнi, мають нерiвнiсть, що є меншою, нiж у чистiй водi, тодi як йодовi солi,
 якi мають бiльшу поверхневу спорiдненiсть, мають бiльшу нерiвнiсть. Це передбачає, що iони здаля вiд
 поверхнi та iони поблизу поверхнi впливають на границю роздiлу протилежним чином. This work was supported by the National Science Foundation under contract number CHE-0611679. en Інститут фізики конденсованих систем НАН України Condensed Matter Physics Ion clustering in aqueous salt solutions near the liquid/vapor interface Iонне кластерування у водному розчинi солi поблизу границi роздiлу рiдина/пара Article published earlier |
| spellingShingle | Ion clustering in aqueous salt solutions near the liquid/vapor interface Smith, J.D. Rick, S.W. |
| title | Ion clustering in aqueous salt solutions near the liquid/vapor interface |
| title_alt | Iонне кластерування у водному розчинi солi поблизу границi роздiлу рiдина/пара |
| title_full | Ion clustering in aqueous salt solutions near the liquid/vapor interface |
| title_fullStr | Ion clustering in aqueous salt solutions near the liquid/vapor interface |
| title_full_unstemmed | Ion clustering in aqueous salt solutions near the liquid/vapor interface |
| title_short | Ion clustering in aqueous salt solutions near the liquid/vapor interface |
| title_sort | ion clustering in aqueous salt solutions near the liquid/vapor interface |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/155802 |
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