Electrical double layer forces. A Monte Carlo study

Abstract

Using a novel method the force between two charged surfaces with an intervening electrolyte solution has been determined from Monte Carlo simulations. We find large deviations from the standard Poisson–Boltzmann treatment of the so called double layer force for divalent counterions at high surface charge densities and at short separations. The deviations have two causes: (i) Due to the inclusion of the effect of ion–ion correlations the counterions concentrate more towards the charged wall reducing the overlap between the double layers; and (ii) correlated fluctuations in the ion clouds of the two surfaces lead to an attractive interaction of a van der Waals type. For some realistic values of the parameters the attraction overcomes the repulsive part and there is a net attractive force between similarly charged surfaces. This finding leads to a modification of our conceptual understanding of the interaction between charged particles and it shows that the DLVO theory is qualitatively deficient under some, realistic, conditions.

Onset of Cohesion in Cement Paste

“…The failure of the "Ca 2+ bridge" model casts a doubt on the hypothesis of a chemical binding of Ca 2+ ions to the surfaces. The failure of the "ionic clouds" model (mean field) is not surprising, since such an approach is known to fail in conditions of high surface charge density and high ionic concentrations, especially so when the counterions are multivalent [7,8].…”

“…However, we cannot use a mean field approximation, as is done in the PoissonBoltzmann equation; instead, the model must be solved exactly. This can be accomplished with, for instance, Monte Carlo (MC) simulations, where ion-ion correlations are taken into account [7,8]. For instance, an excess of positive charge at one location, near the surface of a particle, may be correlated with a lack of positive charge at the corresponding location near the opposing surface.…”

“…For instance, an excess of positive charge at one location, near the surface of a particle, may be correlated with a lack of positive charge at the corresponding location near the opposing surface. It has already been demonstrated that such correlations can give rise to attractive forces [7][8][9][10][11][12][13].…”

“…The excess osmotic pressure of the interstitial solution may be calculated from the ionic distributions according to either of the two following expressions [7]:…”

Anomalous Protein–Protein Interactions in Multivalent Salt Solution

“…[4][5][6][7][8][9][10][11][12][13] The mechanism relies mainly on strong spatial correlations between ions adsorbed at the surface of the macromolecule, a feature which is not taken into account by generic mean-field theories. [1][2][3][14][15][16] Human Serum Albumin (HSA) is a 585 residues long, 66.5 kDa protein, which is involved in the transport of diverse molecules in blood plasma. 17 HSA solutions undergo reentrant condensation upon addition of trivalent salts (YCl 3 , LaCl 3 , FeCl 3 , or AlCl 3 ).…”