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

Interactions between Silica Particles in the Presence of Multivalent Coions

Forces between charged silica particles in solutions of multivalent coions are measured with colloidal probe technique based on atomic force microscopy. The concentration of 1:z electrolytes is systematically varied to understand the behavior of electrostatic interactions and double-layer properties in these systems. Although the coions are multivalent the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory perfectly describes the measured force profiles. The diffuse-layer potentials and regulation properties are extracted from the forces profiles by using the DLVO theory. The dependencies of the diffuse-layer potential and regulation parameter shift to lower concentration with increasing coion valence when plotted as a function of concentration of 1:z salt. Interestingly, these profiles collapse to a master curve if plotted as a function of monovalent counterion concentration

A Simple Method to Determine Critical Coagulation Concentration from Electrophoretic Mobility

Critical coagulation concentration (CCC) is a key parameter of particle dispersions, since it provides the threshold limit of electrolyte concentrations, above which the dispersions are destabilized due to rapid particle aggregation. A computational method is proposed to predict CCC values using solely electrophoretic mobility data without the need to measure aggregation rates of the particles. The model relies on the DLVO theory; contributions from repulsive double-layer forces and attractive van der Waals forces are included. Comparison between the calculated and previously reported experimental CCC data for the same particles shows that the method performs well in the presence of mono and multivalent electrolytes provided DLVO interparticle forces are dominant. The method is validated for particles of various compositions, shapes, and sizes

Microstructural analysis of Bulk Molding Compounds and correlation with the flexural strength

In this study, the influence of the glass fiber (GF) content on the microstructure and flexural strength of bulk molding compounds (BMCs) is investigated. Three sets of BMCs with different weight fractions of GF (5/10/12.5 wt%) were commercially prepared and compression molded into test specimens. The microstructure of the composites was analysed by scanning electron microscopy and further quantitatively characterized by Voronoi analysis in order to define the degree of the fiber distribution homogeneity. The experimental results were compared to the modelled microstructures. The results revealed that the fiber distribution in the composite with 5 wt% of GF is considered as the most homogeneous. Through the obtained microstructural descriptors, the fiber weight content and their distribution were correlated to the flexural strength of BMCs. The flexural strength was the highest for the composite with 10 wt% of GF

Surfactant mediated particle aggregation in nonpolar solvents

The aggregation behavior of particles in nonpolar media is studied with time-resolved light scattering. At low surfactant concentrations particles are weakly charged and suspensions are not stable. The suspensions become progressively more stable with increasing surfactant concentration as particles become more highly charged. At high concentrations the particles become neutralized and aggregation is again fast. The theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO) is able to predict the stability ratios quantitatively by using the experimentally measured surface charges, screening lengths and van der Waals forces