Screening length for finite-size ions in concentrated electrolytes

Abstract

The classical Debye-Hückel (DH) theory clearly accounts for the origin of screening in electrolyte solutions and works rather well for dilute electrolyte solutions. While the Debye screening length decreases with the ion concentration and is independent of ion size, recent surface-force measurements imply that for concentrated solutions, the screening length exhibits an opposite trend; it increases with ion concentration and depends on the ionic size. The screening length is usually defined by the response of the electrolyte solution to a test charge, but can equivalently be derived from the charge-charge correlation function. By going beyond DH theory, we predict the effects of ion size on the charge-charge correlation function. A simple modification of the Coulomb interaction kernel to account for the excluded volume of neighboring ions yields a non-monotonic dependence of the screening length (correlation length) on the ionic concentration, as well as damped charge oscillations for high concentrations.

Correlation Length in Concentrated Electrolytes: Insights from All-Atom Molecular Dynamics Simulations

“…28 The lower exponent (and corresponding smaller decay length) is, however, in good agreement with previous theoretical results, with reported exponents ranging between 1 and 2. 34,36,37,39 As an illustration of such predictions of liquid state theories, Fig.4 We note that in the high-concentration regime, all the theoretical decay lengths correspond to an oscillatory decay, while no such oscillations are observed in the experimental force profiles. However, it should be remembered here that surface force experiments do not directly measure the bulk correlation length, but forces between confined interfaces.…”

“…were obtained using a simple model based on the modification of the Coulomb interaction, though again without reproducing the experimentally observed value of ↵. 37 Finally, within this current environment, Kjellander further expanded his Dressed Ion Theory in an attempt to describe the experimental observations. 38,39 At present, however, it cannot be ruled out that liquid state theories based on simple descriptions of electrolytes such as the (restricted) primitive model cannot correctly capture the behavior of experimental systems.…”

Structuring of colloidal silica nanoparticle suspensions near water–silica interfaces probed by specular neutron reflectivity

“…Such exponentially damped oscillatory profile is expected due to the appearance of complex poles determining the decay of correlations in hard-sphere and charged particle fluids. [16][17][18] To obtain a quantitative fit of the neutron data, it was necessary to introduce a particle-free layer containing pure water of thickness d next to the water-silica interface. Such a particle-free layer should occur due to electrostatic repulsion between the charged particles and the like-charged interface and its existence has further been suggested on theoretical grounds.…”

“…10,11,14,15 Numerous theoretical studies suggest that similar layered structures should also form near isolated interfaces in hard-sphere or charged colloidal suspensions. [16][17][18][19] However, the experimental evidence is scarce. We are only aware of two X-ray reflectivity studies addressing this issue.…”

Stability of ionic liquid modeled by composite Coulomb-Yukawa potentials

“…Other systematic modeling efforts employ computer simulations [10] or use density functional theory [11][12][13]. There is also a class of models that attempt to incorporate ion-ion correlations and still preserve the conceptual simplicity of mean-field approaches [14][15][16][17][18][19][20][21]. A premier example for the latter is the incorporation of a nonlocal dielectric constant by Bazant, Storey, and Kornyshev (BSK) [22] into the lattice-based [23] mean-field model of the EDL.…”