Effect of Cation Size and Charge on the Interaction between Silica Surfaces in 1:1, 2:1, and 3:1 Aqueous Electrolytes

Abstract

Application of two complementary AFM measurements, force vs separation and adhesion force, reveals the combined effects of cation size and charge (valency) on the interaction between silica surfaces in three 1:1, three 2:1, and three 3:1 metal chloride aqueous solutions of different concentrations. The interaction between the silica surfaces in 1:1 and 2:1 salt solutions is fully accounted for by ion-independent van der Waals (vdW) attraction and electric double-layer repulsion modified by cation specific adsorption to the silica surfaces. The deduced ranking of mono- and divalent cation adsorption capacity (adsorbability) to silica, Mg(2+) < Ca(2+) < Na(+) < Sr(2+) < K(+) < Cs(+), follows cation bare size as well as cation solvation energy but does not correlate with hydrated ionic radius or with volume or surface ionic charge density. In the presence of 3:1 salts, the coarse phenomenology of the force between the silica surfaces as a function of salt concentration resembles that in 1:1 and 2:1 electrolytes. Nevertheless, two fundamental differences should be noticed. First, the attraction between the silica surfaces is too large to be attributed solely to vdW force, hence implying an additional attraction mechanism or gross modification of the conventional vdW attraction. Second, neutralization of the silica surfaces occurs at trivalent cation concentrations that are 3 orders of magnitude smaller than those characterizing surface neutralization by mono- and divalent cations. Consequently, when trivalent cations are added to our cation adsorbability series the correlation with bare ion size breaks down abruptly. The strong adsorbability of trivalent cations to silica contrasts straightforward expectations based on ranking of the cationic solvation energies, thus suggesting a different adsorption mechanism which is inoperative or weak for mono- and divalent cations.

Quantifying Specific Ion Effects on the Surface Potential and Charge Density at Silica Nanoparticle–Aqueous Electrolyte Interfaces

“…This result is consistent with the original zeta-potential work of Kosmulski, 18 who concluded anion effects are insignificant, and the AFM work of Sivan and coworkers who noted no difference in the force distance curves between NaCl and NaBr electrolytes up to 200 mM. 62 All of these results are, however, at odds with the pronounced specific anion effects on the relative surface potentials of silica substrates reported by SHG. 25 Recently, Haber and coworkers postulated that SHG might be a measure of the zeta-potential, and not the surface potential.…”

Forces between Negatively Charged Interfaces in the Presence of Cationic Multivalent Oligoamines Measured with the Atomic Force Microscope

“…Such an additional attractive force probably occurs quite universally in the presence of multivalent counterions, since similar additional forces were reported for latex particles in the presence of simple trivalent and tetravalent ions, 12,44 and for silica surfaces in the presence of trivalent cations. 7 Modeling with DLVO Theory. The measured force profiles were modeled with DLVO theory quantitatively.…”

The Human Mitochondrial DNA Depletion Syndrome Gene MPV17 Encodes a Non-selective Channel That Modulates Membrane Potential

“…3D). An opposite ion selectivity of the MPV17 channel in CaCl 2 versus KCl solution is not surprising because the hydrated radius of the Ca 2ϩ ion is significantly larger than that of the K ϩ ion (29,30). When measurements were made without reducing agents such as DTT, the channel was resistant to closing in the range of holding potentials of Ϯ100 mV (Fig.…”