Attractive Double Layer Interactions Research Articles

Ultrathin Wetting Films on Hydrophilic Titania Surfaces: Equilibrium and Dynamic Behavior

Colloid probe atomic force microscopy experiments were carried out between a titania particle and an air bubble in KCl solutions. The surface charges of both the bubble and the particle were controlled by varying the electrolyte concentration and pH of the solution. In all experiments, the bubbles were negatively charged while the titania particles were either negatively (above the pH of the point of zero charge, pHPZC) or positively (below pHPZC) charged. The experimental results have been compared with a theoretical model of the thin-film drainage to investigate the effect of repulsive van der Waals interactions and attractive double layer interactions in promoting hysteresis and hydrodynamic pull-off forces in dynamic particle–bubble interactions. This is the first such system we are aware of that has been analyzed at this level of detail: most of the previous studies have dealt with stable films under a repulsive disjoining pressure or unstable films under an attractive disjoining pressure. The outcomes of this study are important in fields as diverse as water treatment, mineral flotation, and biology.

Hydrodynamic field effect on brownian particles deposition in porous media

Abstract In the present paper, the Brownian dynamic simulation method is applied to study the initial deposition behavior of colloidal particles onto the collector surfaces in a filtration bed. By using four different porous media models, Kuwabara, Happel and N–M model I (when Darcy's equation is adopted) and N–M model II (when Brinkman's equation is adopted), to characterize the flow field around the collector, the effects of the total interaction energy curves of various shapes and the magnitudes of the porosity of porous media on the collection efficiencies of Brownian particles are examined. Under the same simulation condition, it is found that the highest collection efficiency is always obtained when the N–M model I is used in the Brownian dynamic simulation of the present paper. Comparing with the published experimental data of measuring the deposition rates of Brownian particles, it is found that the simulation model of the present paper can give a good simulation result for the experiment of the attractive double layer interactions. Disparities between theoretical predictions and experimental data are observed for the experiment of the repulsive double layer interactions at the unfavorable deposition region.

Particle deposition behavior simulated by the stochastic method

The deposition of colloidal particles onto the collector surface in two-dimensional flows is studied using the Brownian dynamics simulation method. By using the Kuwabara model to characterize the flow field, the effects of the total interaction energy curves of various shapes on the collection efficiencies of Brownian particles are examined. The simulation results are tested against published experimental data of the deposition rates of Brownian particles, for the cases of the repulsive double layer interactions (Elimelech, M., O'Melia, R.C., 1990. Effect of particle size on collision efficiency in the deposition of Brownian particles with electrostatic energy barriers. Langmuir, 6 (6) 1153–1163.) and of the attractive double layer interactions (Elimelech, M., 1991. Kinetics of capture of colloidal particles in packed beds under attractive double layer interactions. J. Colloid Interface Sci., 146 (2), 337–352). The simulation results with the Brownian diffusion taken into account in the particle deposition mechanisms give a better fit with these experimental data than that obtained without considering the Brownian diffusion.

Charge inversion in electric double layers and effects of different sizes for counterions and coions

The molecular mechanisms behind the phenomena of charge inversion in the diffuse electric double layer (i.e., inversion of sign in the charge distribution profile) and attractive double-layer interactions between equally charged surfaces have been investigated with statistical mechanical methods. In aqueous systems with monovalent electrolytes these phenomena can, for example, be induced by having larger coions than counterions, while for divalent electrolytes they occur primarily for electrostatic reasons. We have identified several different mechanisms for the charge inversion. In one of the mechanisms, which only occurs at low surface charge density, the different distances of closest approach to the surface for the ions are crucial, while in some other mechanisms active in the monovalent systems the different size in the ion–ion interaction is the important factor. For divalent electrolytes the electrostatic part of the ion–ion correlations is the dominating effect and ion sizes are not as important, while in the monovalent case core–core collisions between the ions play a very important role.

Theoretical simulation of the collection efficiencies of brownian particles

The deposition problem of colloidal particles onto the collector surface in two-dimensional flows is studied using the Brownian dynamics simulation method. With the Kuwabara model for characterizing the flow field, the effects of the total interaction energy curves of various shapes on the collection efficiencies of Brownian particles are examined. Comparing with the experimental data of measuring the deposition rates of Brownian particles, it is found that the deposition model of the present paper can give a better simulation result than the previous convective diffusion model for the experiment of the repulsive double layer interactions [M. Elimelech and R.C. O'Melia, Langmuir, 6 (1990) 1153], and an opposite result is obtained for the experiment of the attractive double layer interactions [M. Elimelech, J. Colloid Interface Sci., 146 (1991) 337].

Ion‐ion correlations and effective charges in electrolyte and macroion systems

AbstractVarious ion‐ion correlation mechanisms that affect double layer interactions between charged macroparticles in electrolyte solutions are reviewed and discussed. Such effects give rise to quantitative and sometimes qualitative deviation from the prediction of the Poisson‐Boltzmann theory. Special attention is given to the attractive double layer interactions that can appear between equally charged surfaces at short surface separations for aqueous systems with divalent counterions. The long‐range behaviour of the double layer interaction is also treated. It is efficiently described in terms of effective surface charge densities, which summarizes how the inner parts of the diffuse double layer affects the distant parts. The magnitude as well as the sign of the effective charge depends on the state of the system. Charge reversal can occur for aqueous systems with divalent counterions. A major objective of the paper is to describe and illustrate the mechanisms in a simple and graphical manner.

Effect of Particle Size on the Kinetics of Particle Deposition under Attractive Double Layer Interactions

The effect of particle size on the kinetics of particle deposition in the presence of attractive double layer interactions has been studied theoretically and experimentally. Particle deposition experiments were carried out with several model suspensions of positively charged latex particles and negatively charged glass beads using the packed bed column technique. The model particles used in the deposition experiments covered a wide size range, from 0.08 to 2.51 μm. Experimental deposition rates were compared to theoretical predictions based on a numerical solution of the convective diffusion equation with colloidal, hydrodynamic, and gravitational forces fully incorporated. Theoretical and experimental results reveal that the enhancement in particle deposition rate (i.e,, the deposition rate in the presence of double layer interaction divided by the rate in the absence of double layer interaction) is dependent on particle size. At low ionic strengths, the enhancement in deposition rate passes through a maximum as the particle size increases. This maximum corresponds to particles with a size around 1 μm. It is also concluded that this maximum is determined by the interplay between the size of the particles and the range of the attractive double layer interactions.

Kinetics of capture of colloidal particles in packed beds under attractive double layer interactions

The kinetics of capture of suspended colloidal particles in a packed bed of granular material in the presence of attractive double layer interactions have been investigated. Colloid deposition experiments were carried out with positively charged polystyrene latex colloids and negatively charged glass beads packed in a laboratory scale column. A notable increase in colloid deposition rates was observed when the ionic strength of the aqueous solution was reduced from 0.1 M to a value of 10 −6−10 −5 M. The experimental results were generally in good agreement with theoretical deposition rates, which were calculated from a numerical solution of the convective diffusion equation with colloidal and hydrodynamic interactions fully incorporated. The enhancement of the colloid deposition rates is attributed to the increase in the range and magnitude of the attractive double layer interactions as the ionic strength decreases. When attractive double layer interactions extend to large distances from the collector surface, the transport of particles toward the collector increases beyond that of pure convective diffusion, and, as a result, colloid deposition rates also increase.

Attractive double-layer interactions between calcium clay particles

The mechanism responsible for restricted swelling of calcium clays in water and in aqueous salt solutions is examined. Particular attention is given to the montmorillonite, vermiculite, and illite systems. The diffuse double-layer interactions are calculated using an advanced statistical mechanical method, the Anisotropic Hypernetted Chain approximation. In contrast to the predictions of the simple Poisson-Boltzmann theory, which is based on inadequate approximations, for divalent ions the double-layer interaction is strongly attractive at relatively small surface separations, provided the density of surface charge is reasonably large. The attraction is a consequence of the correlations between the ions, giving rise to an electrostatic fluctuation force. When the van der Waals forces between the dielectric media are included, the attraction becomes even larger. The attractive force between the Ca-clay particles gives rise to a stable state, a potential minimum. No specific binding or hydration effects involving the Ca 2+ ions are needed to explain the existence of the minimum. However, the position of the potential minimum as derived using the model, based on diffuse double-layer and van der Waals forces only, is influenced by hydration interactions. Some implications of the potential minimum are discussed.