Forces between silica particles in the presence of multivalent cations

Abstract

Forces between negatively charged silica particles in aqueous electrolyte solutions were measured with the colloidal probe technique based on the atomic force microscope (AFM). The present study focuses on the comparison of monovalent and multivalent counterions, namely K(+), Mg(2+), and La(3+). The force profiles can be well described with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) down to distances of about 4 nm. At smaller distances, the forces become strongly repulsive due to additional non-DLVO repulsion. In the presence of La(3+), one observes an additional attractive force with a range of about 1 nm at intermediate salt concentrations. This force is probably related to ion-ion correlations, but could also be influenced by surface charge heterogeneities or charge fluctuation forces.

Molecular insight into the nanoconfined calcite–solution interface

“…The surface forces were modeled by the DLVO theory with an experimental Hamaker constant of 2.8 × 10 −21 J (20) for separations larger than 5 nm and under the assumption of constant charge regulation with an effective radius of R eff = R/2 (see details in SI Appendix). The EDL significantly collapses in both 10 and 100 mM, in agreement with previous work with calcium and other multivalent ions (20,25). Hydration forces with at most two FTTs were resolved at all of the investigated concentrations (Fig.…”

“…proven to be reliable and powerful to directly measure surface forces (19,20). The DLVO theory describes well the long-range interactions between the confining surfaces despite calcite's unconventional Stern layer.…”

Interactions between charged particles with bathing multivalent counterions: experiments vs. dressed ion theory

“…CoHex, spermine, and spermidine [48,49,59]. More recently, colloidal probe AFM was set up to study the forces between a colloidal particle and a surface or two either similar or dissimilar colloidal particles of negative or positive surface charge in the presence of multivalent counterions [60][61][62][63][64][65][66][67]. Some measurements were also done in the presence of multivalent coions, however these interactions are not the focus of the present paper [68].…”

“…Sivan and coworkers [61,62] have observed an exponential short-range attraction between two silica surfaces in the presence of trivalent counterions near charge neutralization, with decay lengths of a few nanometers that were stronger than the estimated vdW forces. Further experimental work performed within the Borkovec group concentrated on a more detailed comparison with the mean-field PB calculations of the DL interactions [63][64][65][66]69]. The main conclusions stemming from these experimental endeavours elucidating the forces in the presence of multivalent counterions can be summarized as follows: The long-range separation behavior of the experimental forces can be accurately described by the PB theory, however, the effective or the renormalized surface potentials and/or charges must be used to accurately describe the data [63][64][65][66]69].…”

“…below a few nanometers, additional attractive forces are observed that cannot be captured within the DLVO framework. While these attractive forces can be approximated phenomenologically by an exponential dependence on the separation, their physical origin remains elusive and their source could be and indeed has been variously attributed to ion-ion correlations, finite ionic size, image-charge interactions, charge heterogeneities, or charge fluctuations [60][61][62][63][64][65][66]71].…”