Abstract
Self-consistent theory for concentrated electrolytes is developed. Oscillatory decay of the charge–charge correlation function with the decay length that shows perfect agreement with the experimentally discovered and so far unexplained scaling is obtained. For the density–density correlations, monotonic asymptotic decay with the decay length comparable with the decay length of the charge correlations is found. We show that the correlation lengths in concentrated electrolytes depend crucially on the local variance of the charge density.
Highlights
The solvation force acting on the plates confining electrolytes decays with increasing distance between the plates with the decay length λS equal to the correlation length in the bulk
The results of experimental measurements for dilute electrolytes confirm that the decay length is equal to the Debye screening length, λD, in perfect agreement with theoretical predictions. λD decreases with increasing concentration of ions, ρ
The scaling exponents found in these studies as well as in all-atom molecular dynamics simulations [12, 13] appeared to be significantly lower than the experimentally measured one
Summary
The solvation force acting on the plates confining electrolytes decays with increasing distance between the plates with the decay length λS equal to the correlation length in the bulk. We consider dimensionless charge and number density of ions in mesoscopic regions around r, c(r) = ρ+(r)−ρ−(r) and ρ(r) = ρ+(r)+ρ−(r) respectively. We make the approximation −T S = drfh(c(r), ρ(r)), where fh(c, ρ) is the free-energy density corresponding to the entropy of mixing of ions and solvent, βfh(c, ρ) = ρ+ ln ρ+ + ρ− ln ρ− + (ρtot − ρ) ln(ρtot − ρ), where β = 1/kBT , with kB the Boltzmann constant.
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