Ion-ion correlation and charge reversal at titrating solid interfaces

Confronting grand canonical titration Monte Carlo simulations (MC) with recently published titration and charge reversal (CR) experiments on silica surfaces by Dove et al. and van der Heyden it et al, we show that ion-ion correlations quantitatively explain why divalent counterions strongly promote surface charge which, in turn, eventually causes a charge reversal (CR). Titration and CR results from simulations and experiments are in excellent agreement without any fitting parameters. This is the first unambiguous evidence that ion-ion correlations are instrumental in the creation of highly charged surfaces and responsible for their CR. Finally, we show that charge correlations result in "anomalous" charge regulation in strongly coupled conditions in qualitative desagreement with its classical treatment.Comment: 4 pages, 4 figures, submitted to PR

Forces between Colloidal Particles in Aqueous Solutions Containing Monovalent and Multivalent Ions

The present article provides an overview of the recent progress in the direct force measurements between individual pairs of colloidal particles in aqueous salt solutions. Results obtained by two different techniques are being highlighted, namely with the atomic force microscope (AFM) and optical tweezers. One finds that the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) represents an accurate description of the force profiles even in the presence of multivalent ions, typically down to distances of few nanometers. However, the corresponding Hamaker constants and diffuse layer potentials must be extracted from the force profiles. At low salt concentrations, double layer forces remain repulsive and may become long ranged. At short distances, additional short range non-DLVO interactions may become important. Such an interaction is particularly relevant in the presence of multivalent counterions.Comment: Submitted on 30th of May 2016 as invited article to Curr. Opinion Colloid Interf. Sci. Edited by W. Ducker and P. Claesson. 15 Pages, 7 Figures 82 reference

Microscopic Protonation Mechanism of Branched Polyamines: Poly(amidoamine) versus Poly(propyleneimine) Dendrimers*

The protonation mechanisms of the poly(amidoamine) (PAMAM) andpoly(propyleneimine) (PPI) dendrimers are clarified and related to their molecular structure. The overall proton binding isotherms can be interpreted in terms of a site binding model, which involves a limited number of parameters, and can be used to gain detailed insight in both macroscopic and microscopic protonation mechanisms. The protonation of the PAMAM dendrimers is dominated by the chemical environment of the amine sites, and the sites protonate almost independently leading to protonation mechanism with a characteristic intermediate core-shell structure. In the case of PPI, the protonation is dominated by the electrostatic nearest-neighbor repulsions between the protonated sites, and leads to an intermediate »onion-like« structure where all the odd shells are protonated

Microscopic Protonation Mechanism of Branched Polyamines: Poly(amidoamine) versus Poly(propyleneimine) Dendrimers*

The protonation mechanisms of the poly(amidoamine) (PAMAM) andpoly(propyleneimine) (PPI) dendrimers are clarified and related to their molecular structure. The overall proton binding isotherms can be interpreted in terms of a site binding model, which involves a limited number of parameters, and can be used to gain detailed insight in both macroscopic and microscopic protonation mechanisms. The protonation of the PAMAM dendrimers is dominated by the chemical environment of the amine sites, and the sites protonate almost independently leading to protonation mechanism with a characteristic intermediate core-shell structure. In the case of PPI, the protonation is dominated by the electrostatic nearest-neighbor repulsions between the protonated sites, and leads to an intermediate »onion-like« structure where all the odd shells are protonated

Charging and Aggregation of Positively Charged Colloidal Latex Particles in Presence of Multivalent Polycarboxylate Anions

Colloidal stability and charging behavior of amidine latex particles in the presence of multivalent oligomers of acrylic acid was investigated by electrophoresis and light scattering. The data were interpreted quantitatively with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO) whereby the surface potentials were estimated from electrophoresis. Monomer leads to slow aggregation at low concentrations and to rapid aggregation at high concentrations, as characteristic for simple salts. The oligomers induce a charge reversal of the particles. Close to the isoelectric point (IEP) aggregation is rapid while the suspension becomes stable away from this point. At high oligomer concentrations, the aggregation becomes rapid again. The agreement between DLVO theory and experiment is good close to the IEP. At higher oligomer concentrations, the theory predicts larger stabilities than observed experimentally. While inter-particle forces seem to be well described by DLVO theory near the IEP, additional attractive non-DLVO forces are becoming relevant at higher concentration

Chromatographic Methods and Transport of Chemicals in Soils

Transport of chemicals in soils and groundwater aquifers has become an increasingly important field in hydrology and soil science. Much progress in this field originates from the picture of the soil as a giant chromatography column. Therefore, one uses successfully concepts borrowed from chromatography theory. The applicability of such ideas for the description of the transport of chemicals in the field is reviewed

DLVO Interaction between Colloidal Particles: Beyond Derjaguin’s Approximation

Van der Waals and electrostatic double layer interactions between two colloidal particles are evaluated from the corresponding interaction energies per unit area between two infinite flat plates using a recently developed technique, the surface element integration. Application of the technique to two interacting spheres results in predictions of interaction energies that are substantially more accurate compared to the predictions based on conventional Derjaguin\u27s approximation. The superior results of the technique compared to Derjaguin’s approximation are attributed to the more rigorous consideration of particle curvature effects in the surface element integration technique

Molecular mass dependence of adsorbed amount and hydrodynamic thickness of polyelectrolyte layers.

https://v2.sherpa.ac.uk/id/publication/18031Highly charged polyelectrolytes adsorbed on oppositely charged colloidal particles are investigated by electrophoresis and dynamic light scattering. The dependence of the adsorbed amount and of the hydrodynamic layer thickness on the molecular mass and the salt level is analyzed. The adsorbed amount increases with increasing salt level and decreases with increasing molecular mass. The hydrodynamic layer thickness is independent of the molecular mass at low salt levels, but increases with the molecular mass as a power law with an exponent 0.10 0.01 at high salt. The same behavior was observed for different polyelectrolytes and substrates and therefore is suspected to be generic. Due to semi-quantitative agreement with computer simulations carried out by Kong and Muthukumar in 1998, the observed behavior is interpreted with conformational changes of single adsorbed polyelectrolyte chains