Dispersion Of Charged Particles Research Articles

Characteristic curves and relationships for surface charging parameters of nonelectrolyte-immersed aqueous cavities

Most properties of charged particles’ dispersions are closely related to the amount of charge residing on the surface of particles. Very few works have been done so far to investigate curvature-dependence of surface potential and charge density of dispersed charged particles. Although there are some experimental studies in the literature on this subject, only a few of them have examined the mathematical relationship between particle size and surface charging parameters, resulting in contradictory findings. Indeed, a universal behavior is yet to be inferred from analysis of the outcomes of these studies since they reported either a roughly constant or decreasing trend of surface charge density with increasing particle radius. Unfortunately, the majority of the limited research efforts on surface charging have focused on dispersion of charged particles in aqueous solutions, but there are systems in biological and engineering worlds where an electrolyte solution is encapsulated in the core of charged particles and immersed in a background non-electrolyte medium. In an attempt to fill this scientific gap and gain a better understanding of surface charging, analytical models are developed in the present work for prediction of surface potential, surface charge, and surface charge density for cylindrical and spherical particles in such systems.First, the problem under investigation is non-dimensionalized to facilitate the modeling process, consider the simultaneous effects of key variables, and generalize the results and behaviors. Then, the mutual relationship between every pair of variables is extracted by employing Gauss's law and combining it with the electro-neutrality condition in an aqueous cavity. Afterwards, the resulting generalized seemingly simple, but inherently complex, integral equations are solved to build the characteristic curves and regressed to derive explicit characteristic equations. Finally, the derived characteristic equations are transformed into a dimensional form to obtain simple formulas for explicit calculations of charging parameters on the surface of electrolyte-encapsulating charged particles in terms of easily measurable properties of the electrolyte solution, the size of the cavity, and thermodynamic conditions. This predictive capability of the new models will significantly reduce the time, costs, and efforts required to simultaneously characterize the size and charging parameters of particles because it removes the need for such a challenging measurement as charging parameters are explicitly related to particle size through thermodynamic conditions, as well as available or easy-to-measure properties of the solution.

Modeling and Simulation of Nonmotorized Vehicles’ Dispersion at Mixed Flow Intersections

Interactions between motorized and nonmotorized vehicles have drawn considerable attention from researchers. They are commonly seen at mixed flow intersections where nonmotorized vehicles, without the restriction of lane markers or physical barriers, may disperse into adjacent lanes and thus lead to complex interactions with motorized vehicles. Such a dispersion phenomenon between heterogeneous participants (e-bikes and bicycles as nonmotorized vehicles versus motorized vehicles) is difficult to model. In this paper, we were inspired by the dispersion of charged particles in an electric field and modeled the dispersion phenomenon of go-straight, nonmotorized vehicles at mixed flow intersections accordingly, as it was discovered in this research that these two dispersion phenomena share three underlying commonalities with each other. A novel particle dispersion model (PDM) based on a particle’s movement in an electric field is proposed. The model is calibrated and validated using 1,490 high-definition sets of trajectory data for go-straight, nonmotorized vehicles during 43 cycles at two typical mixed flow intersections. The PDM is compared with the social force model (SFM) on their dispersion characteristics that are used to describe the nonmotorized bicycles’ behavior. The results show that the PDM performs better than the SFM with regard to depicting the dispersion characteristic indices of the nonmotorized vehicles, such as the travel time, the dispersion intensity of heterogeneous nonmotorized vehicles, the sectional dispersion degree, and other dispersion characteristics.

Effect of the particle interactions on the structuration and mechanical strength of particulate materials

We investigate the effect of the particles interaction on the mechanical strength of particulate materials. Starting from a dispersion of charged particles, the interparticle force can be modulated by the addition of ionic species. The structuration of the medium is then governed by the competition between drying and gelation processes. Rheological measurements show that addition of ionic species boosts the aggregation dynamics into a solid state and changes the structural properties of the final material. This last point is highlighted by precise measurements of i) the mechanical properties of particulate materials through crack pattern quantification, supported by indentation testing, and ii) the permeation properties during the drying process in a controlled geometry. In particular, these results show a decrease of the drained elastic modulus and an increase in the pore size when the ionic species content in the particulate material is increased. Hence, we show that the solid structure behaves mechanically as a network whose pore size increases when the electrostatic repulsion between particles is decreased. These results are consistent with the fact that the way particulate materials are structured determines their mechanical properties.

An experimental study on colloidal crystals formed in two-component dispersion of charged particles

Characterization of colloidal crystals composed of two types of polystyrene particles of different sizes (94 nm and 141 nm respectively) at different number ratios is studied by means of Kossel diffraction and reflection spectra technique. The results showed the dependence of the mean interparticle distance (D0) and crystal structure on the number ratio of the two types of particles. The formation time of crystals lengthens as the number ratio of the two components approaches 1∶1. When the number ratio (9 4nm∶141 nm) decreases, the mean interparticle distance (D0) becomes larger. This study also shows that when the above number ratio equals 5:1, superlattice structure appears in the binary colloidal system.

Interpretation of Light Scattering Spectra of Dispersions – A Hybrid Approach to Account for Interparticle Interactions

AbstractThe problem of extracting quantitative information on individual particle properties from spectroscopic measurements conducted at concentrations where particle interactions become significant is of great industrial and theoretical importance. For dispersions of charged particles, this can happen at fairly low concentrations. The effect of the fluid (slurry) structure has to be taken into account to interpret the light scattering spectra of such dispersions. In this paper, a hybrid method that addresses the effect of the fluid structure is proposed. The hybrid approach describes the fluid structure by relating the “effective” Percus‐Yevick hard‐sphere parameters to the system parameters using empirical models. The feasibility of this approach is examined through a theoretical study with data generated by Monte Carlo simulations of a monodisperse dispersion of charged spherical particles using realistic interaction potentials under single scattering conditions.

Small-Angle Neutron Scattering Study of Concentrated Colloidal Dispersions: The Electrostatic/Steric Composite Interactions between Colloidal Particles

Small-angle neutron scattering was used to investigate the interactions in concentrated colloidal dispersions containing silica or polystyrene latex with adsorbed polyethyleneoxide (PEO). In these dispersions of charged particles, both electrostatic and steric repulsions are present. The PEO layer was made invisible to neutrons through contrast matching. The effect of the interparticle repulsion was clearly shown in the scattering spectra by the appearance of a peak at low Q. The effective potentials can be well described by the Hayter-Penfold/Yukawa (HPY) potential. In the silica dispersions studied, the layer thickness is small, hence the electrostatic potential dominates and the potential has a lower concentration dependence. In the dispersions of polystyrene latex, the adsorbed layer is thicker; consequently, the electrostatic potential dominates at low volume fraction (the potential has a lower concentration dependence), and the steric potential dominates at higher volume fraction (the potential has a higher concentration dependence). This study also suggests that when more than one potential is present the stronger one has a dominant influence in determining the structure factor. This finding makes it possible to describe the multicomponential interactions by a single function.

Aqueous Sol−Gel Process in the Silica−Metasilicate System. A Microrheological Study

The electrochemical quartz crystal microbalance (EQCM) was used to investigate the sol−gel process from an aqueous sodium metasilicate solution at 25 °C and pH 3. From the EQCM data it was possible to obtain information on the changing rheological properties of the system during the whole process. Besides sensing changes in the rheological properties, the EQCM detected film formation on the sensor surface. This additional information was used to estimate, using a model for film formation kinetics, the sol particle size (the model prediction was confirmed by light scattering measurements). The particle size estimation was of importance in the analysis of the sol viscosity behavior during the earlier stages of the particle aggregation process. The analysis, based on a classical model for the viscosity of a dispersion of charged particles in an electrolyte, provided some insight into the initial aggregation phenomena and microgel formation. Determination of the gelling point was made by examining the evoluti...

Diffusion and light scattering in dispersions of charged particles with thin electrical double layers

The perturbation approach of Barker and Henderson is applied to obtain analytical formulae for the collective diffusion coefficient, short-time self-diffusion coefficient, sedimentation velocity, static and dynamic structure factors at low particle concentration. All these quantities are expressed as explicit functions of the system parameters (particle size and charge, electrolyte concentration, Hamaker constant, etc.) and can be easily calculated if the latter are known. By using light scattering experiments information on the particle charge (or potential) and Hamaker constant can be obtained.

Light scattering study of dynamic and time-averaged correlations in dispersions of charged particles

Several aqueous dispersions of charged polystyrene spheres (mean radius =250 aa) have been studied at very low ionic strength by conventional light scattering and photon correlation spectroscopy. Plotted as a function of scattering angle, the mean scattered intensity exhibited maxima similar to those found in the structure factor of simple liquids determined by X-ray or neutron scattering. Fourier transformation of the corrected intensity data yielded radial distribution functions whose structure indicated considerable short-range ordering of the particles due to repulsive coulombic interactions. The reciprocal of the effective particle diffusion coefficient (determined from the initial decay rate of the non-exponential temporal autocorrelation function of the scattered light field) showed angular dependence similar to the mean intensity, in agreement with recent theoretical predictions.

Dispersion of Charged Particles in a Turbulent Air Stream under Transverse Flow Conditions

Dispersion of Charged Particles in a Turbulent Air Stream under Transverse Flow Conditions

Magnetic field distribution for weak-, strong- and FFAG-focusing particle accelerators and other nuclear instruments

For the magnetic guiding field of the weak-, strong-, and FFAG-focusing nuclear instruments used in the acceleration or dispersion of charged particles, general analytic expressions, valid for any point of the magnet gap, are derived concerning the following parameters: magnetic scalar potential, magnetic induction and magnetic vector potential. These expressions are useful for the study of particle motion as well as for pole face design.