TY - JOUR
T1 - Theory of electrolytes including steric, attractive, and hydration interactions
AU - Okamoto, Ryuichi
AU - Koga, Kenichiro
AU - Onuki, Akira
N1 - Funding Information:
R.O. would like to thank Tomonari Sumi for informative discussions. R.O. acknowledges support from the JSPS KAKENHI (Grant Nos. JP18K03562 and JP18KK0151). K.K. acknowledges support from the JSPS KAKENHI (Grant Nos. JP18KK0151 and JP20H02696). A.O. would like to thank Zhen-Gang Wang for informative correspondence.
Publisher Copyright:
© 2020 Author(s).
PY - 2020/8/21
Y1 - 2020/8/21
N2 - We present a continuum theory of electrolytes composed of a waterlike solvent and univalent ions. First, we start with a density functional F for the coarse-grained solvent, cation, and anion densities, including the Debye-Hückel free energy, the Coulombic interaction, and the direct interactions among these three components. These densities fluctuate obeying the distribution ∞exp(-F/kBT). Eliminating the solvent density deviation in F, we obtain the effective non-Coulombic interactions among the ions, which consist of the direct ones and the solvent-mediated ones. We then derive general expressions for the ion correlation, the apparent partial volume, and the activity and osmotic coefficients up to linear order in the average salt density ns. Second, we perform numerical analysis using the Mansoori-Carnahan-Starling-Leland model [J. Chem. Phys. 54, 1523 (1971)] for three-component hardspheres. The effective interactions sensitively depend on the cation and anion sizes due to competition between the steric and hydration effects, which are repulsive between small-large ion pairs and attractive between symmetric pairs. These agree with previous experiments and Collins' rule [Biophys. J. 72, 65 (1997)]. We also give simple approximate expressions for the ionic interaction coefficients valid for any ion sizes.
AB - We present a continuum theory of electrolytes composed of a waterlike solvent and univalent ions. First, we start with a density functional F for the coarse-grained solvent, cation, and anion densities, including the Debye-Hückel free energy, the Coulombic interaction, and the direct interactions among these three components. These densities fluctuate obeying the distribution ∞exp(-F/kBT). Eliminating the solvent density deviation in F, we obtain the effective non-Coulombic interactions among the ions, which consist of the direct ones and the solvent-mediated ones. We then derive general expressions for the ion correlation, the apparent partial volume, and the activity and osmotic coefficients up to linear order in the average salt density ns. Second, we perform numerical analysis using the Mansoori-Carnahan-Starling-Leland model [J. Chem. Phys. 54, 1523 (1971)] for three-component hardspheres. The effective interactions sensitively depend on the cation and anion sizes due to competition between the steric and hydration effects, which are repulsive between small-large ion pairs and attractive between symmetric pairs. These agree with previous experiments and Collins' rule [Biophys. J. 72, 65 (1997)]. We also give simple approximate expressions for the ionic interaction coefficients valid for any ion sizes.
UR - http://www.scopus.com/inward/record.url?scp=85089794457&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85089794457&partnerID=8YFLogxK
U2 - 10.1063/5.0015446
DO - 10.1063/5.0015446
M3 - Article
C2 - 32828079
AN - SCOPUS:85089794457
VL - 153
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 7
M1 - 15446
ER -