Structures of Water Molecules at the Interfaces of Aqueous Salt Solutions and Silica: Cation Effects

We have studied the infrared spectra of H2O, D2O, and HDO in hydrated Nafion membranes in the sodium form. The spectrum of isotopically isolated HDO exhibits two distinct absorption bands in the OH stretching region and similarly in the OD stretching region. These bands have been taken to correspond to two distinct environments of the OH groups in Nafion, identified as [Formula: see text] and[Formula: see text]. It appears that a substantial proportion of water molecules have an OH group (or occasionally both OH groups) exposed to the fluorocarbon environment. This implies that the hydrated ion clusters are either much smaller than previously estimated or, more likely, are non-spherical in shape with frequent local intrusions of the fluorocarbon phase. Water in Nafion is much less strongly hydrogen-bonded than water in aqueous salt solutions at the same temperature and may be expected to have distinct physical properties.

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IR study of cation effects on the O-D stretching frequencies of isotopically dilute HDO in aqueous salt solutions

Monatshefte für Chemie - Chemical Monthly ◽

10.1007/bf00811267 ◽

1986 ◽

Vol 117 (8-9) ◽

pp. 977-984 ◽

Cited By ~ 9

Author(s):

Werner Mikenda

Keyword(s):

Salt Solutions ◽

Cation Effects ◽

Aqueous Salt Solutions ◽

Ir Study

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ChemInform Abstract: IR Study of Cation Effects on the O-D Stretching Frequencies of Isotopically Dilute HDO in Aqueous Salt Solutions.

ChemInform ◽

10.1002/chin.198701017 ◽

1987 ◽

Vol 18 (1) ◽

Author(s):

W. MIKENDA

Keyword(s):

Salt Solutions ◽

Cation Effects ◽

Aqueous Salt Solutions ◽

Ir Study

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The behavior of ions in water is controlled by their water affinity

Quarterly Reviews of Biophysics ◽

10.1017/s0033583519000106 ◽

2019 ◽

Vol 52 ◽

Cited By ~ 7

Author(s):

Kim D. Collins

Keyword(s):

Long Range ◽

Short Range ◽

Ion Pairs ◽

Size Exclusion ◽

Water Molecules ◽

Dielectric Relaxation Spectroscopy ◽

Salt Solutions ◽

Electrostatic Forces ◽

Aqueous Salt Solutions ◽

Water Affinity

Abstract The strong, long-range electrostatic forces described by Coulomb's law disappear for ions in water, and the behavior of these ions is instead controlled by their water affinity – a weak, short-range force which arises from their charge density. This was established experimentally in the mid-1980s by size-exclusion chromatography on carefully calibrated Sephadex® G-10 (which measures the effective volume and thus the water affinity of an ion) and by neutron diffraction with isotopic substitution (which measures the density and orientation of water molecules near the diffracting ion and thus its water affinity). These conclusions have been confirmed more recently by molecular dynamics simulations, which explicitly model each individual water molecule. This surprising change in force regime occurs because the oppositely charged ions in aqueous salt solutions exist functionally as ion pairs (separated by 0, 1 or 2 water molecules) as has now been shown by dielectric relaxation spectroscopy; this cancels out the strong long-range electrostatic forces and allows the weak, short-range water affinity effects to come to the fore. This microscopic structure of aqueous salt solutions is not captured by models utilizing a macroscopic dielectric constant. Additionally, the Law of Matching Water Affinity, first described in 1997 and 2004, establishes that contact ion pair formation is controlled by water affinity and is a major determinant of the solubility of charged species since only a net neutral species can change phases.

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State of ions and water molecules in the water salt solutions of polyacrylamide and co-polymer of “acrylamide–acrylic acid Na/k salt”

Doklady of the National Academy of Sciences of Belarus ◽

10.29235/1561-8323-2019-63-6-695-703 ◽

2020 ◽

Vol 63 (6) ◽

pp. 695-703 ◽

Cited By ~ 1

Author(s):

V. S. Soldatov ◽

D. N. Davlyud ◽

T. V. Bezyazychnaya ◽

E. V. Vorobieva ◽

E. G. Kasandrovich ◽

...

Keyword(s):

Acrylic Acid ◽

Water Molecules ◽

Molecular Models ◽

Salt Solutions ◽

Carboxylate Groups ◽

First Case ◽

Aqueous Salt Solutions ◽

Calculation Results ◽

Electronic Parameters ◽

Water Salt

Geometrical and electronic parameters of the microstates of the molecular models of polyacrylamide and co-polymers of acrylamide-acrylic acid in aqueous solutions of sodium and potassium chlorides were computed by the non-empirical SCF MO LCAO method with the use of the basis MINI Huzinaga. The models contained four monomeric units of the polymer, including two metal carboxylate groups, 80 water molecules and two pairs of ions Na+ and Cl– or K+ and Cl–. It follows from the calculation results that there is a principal difference in the hydration of Na+ and K+: the Na+‧‧‧О2– bond is shorter than the sum of the radii of the interacting ions, while the k+‧‧‧O2– bond is equal or longer. This indicates that in the first case, the bonds are partially covalent, while in the second one they are pure electrostatic. All elements of the molecular models in the both cases are combined by the intermolecular bonds forming a spatial net. The polymer molecules have a flexible chain with oxygen containing functional groups that are built into the structure of the salt solutions without distorting it. We assume that this is the main reason for the good solubility of the studied polymers in the aqueous salt solutions.

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