Colloidal particles Agglomeration

The sol-gel reactions have mainly been investigated in alcoholic solution, which is a reaction medium easily allows electrostatic stabilization by propriate choice of the pH. This type of stabilization can only be used in a few cases as a means for incorporating the colloidal particle agglomerate-free into tailored matrices, since these matrices, as a rule, destroy the electrostatic "coating" around the particles. As a consequence, agglomeration takes place, and the high transparency required for optical application is lost For this reason, another type, the so-called short organic molecule stabilization by tailored surface modification for colloidal particles, has been developed, the principles of which in comparison to the electrostatic stabilization is schematically shown in Fig. 14. 

Flocculation Agglomeration of colloidal material by adding a chemical that causes the colloidal particles to produce larger particles. 

The colloidal particles can be crystalline or constitnte an amorphons agglomeration of individual molecnles. The definition also includes nonaggregated large macromolecules such as proteins. An arbitrary distinction is made between hydrophobic colloids (sols) and hydrophilic colloids (gels), which depends on the degree and type of interaction with the aqneons solvent. 

In some cases shape-control has also been achieved tetra( -octyl)ammonium glycolate transforms Pd(N03)2 predominantly into trigonal Pd particles [186]. Recent work has confirmed that the colloidal protective agents not only prevent particle agglomeration but even provide control of the crystal growth during particle synthesis (see e.g., Ref. [187-191]). The drawbacks of this route are the restriction to noble metal salts and the limited industrial availability of A-(octyl)j RC02. 

Each radical transfers an electron to the colloidal particles. One colloidal particle can accept and store a large number of electrons until the aqueous solvent is reduced. Under stationary conditions, a certain number x of electrons reside on a particle, thus producing a negative potential sufficiently high for Hj evolution (n = agglomeration number) ... 

If the volume of solid particles is conserved during agglomeration, the volume fraction of colloidal particles, the volume of colloids per unit volume of suspension, <>, can be expressed as... 

Agglomeration. - The tendency of large molecules or colloidal particles to bunch together, allowing removal from the solution, especially in polymerization process solutions. 

When two similarly charged colloid particles, under the influence of the EDL, come close to each other, they will begin to interact. The potentials will detect one another, and this will lead to various consequences. The charged molecules or particles will be under both van der Waals and electrostatic interaction forces. The van der Waals forces, which operate at a short distance between particles, will give rise to strong attraction forces. The potential of the mean force between colloid particle in an electrolyte solution plays a central role in the phase behavior and the kinetics of agglomeration in colloidal dispersions. This kind of investigation is important in these various industries ... 

Slurry particle agglomeration can take place in the slurry in which abrasive particles and colloids coalesce to form extended particles. 

Asphalt emulsions are dispersions of asphalt in water that are stabilized into micelles with either an anionic or cationic surfactant. To manufacture an emulsion, hot asphalt is mixed with water and surfactant in a colloid mill that produces very small particles of asphalt on the order of 3 pm. These small particles of asphalt are prevented from agglomerating into larger particles by a coating of water that is held in place by the surfactant. If the asphalt particles agglomerate, they could setde out of the emulsion. The decision on whether a cationic or anionic surfactant is used depends on the application. Cationic stabilized emulsions are broken, ie, have the asphalt settle out, by contact with metal or silicate materials as well as by evaporation of the water. Since most rocks are silicate-based materials, cationic emulsions are commonly used for subbase stabilization and other similar applications. In contrast, anionic emulsions only set or break by water evaporation thus an anionic emulsion would be used to make a cold patch compound. 

From a comparison of the two collision frequency terms, described in detail in the Equations 3 and 6, one obtains the relative contributions of the perikinetic and orthokinetic transport to the total particle agglomeration. The ratio is a function of the radius of the colloid, r, and the absolute value of the velocity gradient du/dz ... 

---