Abstract
The structure of aqueous solutions of 1:1 salts (KCl, NaCl, KF, and CsI) near a hydrophobic surface is analysed using the angle-dependent integral equation theory. Water molecules are taken to be hard spheres imbedded with multipolar moments including terms up to octupole order, and hard spherical ions are immersed in this model water. The many-body interactions associated with molecular polarizability are treated at the self-consistent mean field level. The effects of catio nic and anionic sizes and salt concentration in the bulk are discussed in detail. As the salt concentration increases, the layer of water molecules next to the surface becomes denser but its orientational order remains almost unchanged. The concentration of each ion at the surface can be drastically different from that in the bulk. As a striking example, at sufficiently low salt concentrations, the concentration of I is about 500 times higher than that of F at the surface.
Highlights
The aqueous electrolyte solution is an essential constituent of a system in a variety of fields such as solution chemistry, electrochemistry, biophysics, biochemistry, and colloidal science
The many-body interactions associated with molecular polarizability are treated at the self-consistent mean field level [2,3]
The function p(θOH) in figure 1 indicates that at the contact with the surface is a dominant contribution from water molecules oriented with one OH bond directed into the surface: The local maxima occur at θOH ∼ 71◦ and 180◦ [21,22]
Summary
The aqueous electrolyte solution is an essential constituent of a system in a variety of fields such as solution chemistry, electrochemistry, biophysics, biochemistry, and colloidal science. It is not definite if the water-ion electrostatic interaction potentials can be accurately described with the SPC/E model due to the potential impertinence of its multipolar moments In these 20 years, a great progress has been made in constructing the angle-dependent integral equation theories combined with the multipolar water model for aqueous electrolyte solutions in the bulk and at surfaces and in developing the robust numerical solution algorithms [2,3,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. The number densities of water molecules, cations, and anions in each solution are determined from the experimental solution density at 298 K and 1 atm [25,26]
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