Colloidal dispersions charge density

The properties of filtrate reducers contribute to their different molecular structures. Nonionic filtrate reducers work by completely blocking the filter-cake pore, and anionic ones work by increasing the negative-charge density of filter-cakes and decreasing pore size. Anionic species cause further clay dispersion, but nonionic species do not, and both of them are beneficial to colloid stability [1890]. 

Statistical mechanics was originally formulated to describe the properties of systems of identical particles such as atoms or small molecules. However, many materials of industrial and commercial importance do not fit neatly into this framework. For example, the particles in a colloidal suspension are never strictly identical to one another, but have a range of radii (and possibly surface charges, shapes, etc.). This dependence of the particle properties on one or more continuous parameters is known as polydispersity. One can regard a polydisperse fluid as a mixture of an infinite number of distinct particle species. If we label each species according to the value of its polydisperse attribute, a, the state of a polydisperse system entails specification of a density distribution p(a), rather than a finite number of density variables. It is usual to identify two distinct types of polydispersity variable and fixed. Variable polydispersity pertains to systems such as ionic micelles or oil-water emulsions, where the degree of polydispersity (as measured by the form of p(a)) can change under the influence of external factors. A more common situation is fixed polydispersity, appropriate for the description of systems such as colloidal dispersions, liquid crystals, and polymers. Here the form of p(cr) is determined by the synthesis of the fluid. 

Polyacrylic acid stabilised latices have been prepared by aqueous dispersion polymerisation. The method used is analogous to the non-aqueous dispersion (NAD) polymerisation methods originally used to prepare polymethyl methacrylate particles in aliphatic hydrocarbons (1. In effect the components of a NAD polymerisation have been replaced as follows aliphatic hydrocarbon by aqueous alcohol, and degraded rubber, the stabiliser, by polyacrylic acid (PAA). The effect of various parameters on the particle size and surface charge density of the latices is described together with details of their colloidal stability in the presence of added electrolyte. 

In the latter case the total interaction, which is what can be measured, is affected by the net charge of the surface and the adsorbed layer, ion-ion correlations, bridging interactions and steric confinement of the polymer chain [116]. We note that polyelectrolytes are often present as additives in colloidal dispersions and the character of the forces generated by the polyelectrolyte adsorption layers has a paramount influence on stability of these colloidal systems. With the aim to illustrate what can be learnt about polyelectrolyte adsorption layers using the SFA, we will look at the influence of the polyelectrolyte charge density on the forces acting between surfaces coated with polyelectroytes. We will consider an example where the polyelectrolyte charge density is varied by a systematic... 

PUgrimm, H. and Sonntag, H., Determination of surface charge density of dispersed oxidic particles in aqueous solutions by a coulometric method. Colloid Polym. Sci., 258,471, 1980. 

Two effects which may be encountered during nonaqueous electrophoresis are space charge conditions and electrohydrodynamics (EHD). When an electric field is applied across a uniformly dispersed colloid the macroscopic charge density is zero and the field is uniform at the time of application. As the separation of opposite polarity charges occurs, a net internal... 

First measurements of the electrostatic double-layer force with the AFM were done in 1991 [9, 10]. The electrostatic double layer depends on the surface charge density (or the surface potential) and the ionic strength. A brief introduction to the theory of the electrostatic force is given in Chap. 4. The electrostatic double-layer force is in many cases responsible for the stabilization of dispersions. An AFM experiment can be regarded as directly probing the interaction between a sample surface and a colloidal particle (or the AFM tip). Since the AFM tip is relatively small, this interaction can be probed locally. The lateral spacial resolution can be of the order of few nanometers. 

In conclusion, the way polymers influence the stability of lyophobic colloids is far more complicated than the way low molecular weight electrolytes do. Whether polymers stabilize or destabilize, the dispersion is delicately determined by properties and composition of the system (adsorption affinity, solvent quality, particle size, degree of polymerization, charge densities on the particle and the polymer, particle-polymer ratio, ionic strength, presence of divalent ions, and so on) and external conditions, such as the temperature. 

Given the size of clay particles (10-1,000 nm), they are found in solution as colloidal dispersions or gels. At low water content, they can be obtained as dry powders, and can form solid porous materials upon compaction. In all these regimes, their properties crucially depend on the charge density and on the nature of the counterions. Most counterions are mono- or divalent, usually alkaline (most commonly sodium Na" or potassium or alkaline earth cations (most commonly calcium Ca " ). They are not incorporated in the clay layers. Rather, they are located near the surface, either between different layers, in the so-called interlayer porosity, or on the external surfaces of clay stacks (typically 10 layers). Such stacks are called particles, and their assembly to form a porous material then leaves voids called interparticle porosity, with sizes between a few nanometers to tens of nanometers, which are usually saturated by an electrolyte solution. 

Yamanaka, J., Yoshida, H., Koga, T., Ise, N., and Hashimoto, T. (1999). Reentrant order-disorder transition in ionic colloidal dispersions by varying particle charge density. Langmuir 15, 4198-4202. 

Keep in mind that Eqs. (8-14) are only valid for small Kr, when the electrophoresis retardation (electric-field-induced movement of ions in the electric double layer, which is opposite to the direction of particle movement) is unimportant [41J. This limitation is inherent to the Hiickel equation. Practically, a colloidal suspension always contains charged particles dispersed in a medium with surfactants (or electrolytes) of both polarities. In this case the Poisson s equation must be used for deriving the surface charge density and Zeta potential relationship. Under the Dcbyc-Hiickel approximation, i.c., the small value of potential, zey/ kgT, where v is the potential and z is the valency of ion, a simple relationship between the surface charge density and Zeta potential can be easily obtained [7], The Poisson s equation simply says that the potential flux per unit volume of a potential field is equal to the charge density in that area divided by the dielectric constant of the medium. It can be mathematically expressed as ... 

Order (crystal structure)-disorder (liquid structure) transition in ionic colloidal dispersions has been intensively studied [1]. Since the driving force of the ordering is electrostatic, the order-disorder transition point for the colloidal system is largely determined by the surface charge density of the particle and the salt concentration of the dispersion, Cg, in addition to the volume fraction of the particles, . A number of experimental studies have so far been made to determine the transition point as a function of Cs and 0. However, little attention has been paid on the influence of the surface charge density. This seems to be... 

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