Colloidal agglomeration

Some authors distinguish between coagulation and flocculation and use the latter term for colloid agglomeration by bridging of polymer chains. 

Bitea, C., Walther, C., Kim, J. I., Geckeis, H., Rabung, Th., Scherbaum, F. J. Cacuci, D. G. 2003a. Time-resolved observation of Zr02-colloid agglomeration. Colloids Surfaces A, 215, 55-66. 

Equation 9.15 points out that a small increase in particle diameter due to colloid agglomeration has a large impact on the rate of particle settling (Sr). 

Colloids—Agglomerates of atoms or molecules whose sizes are so small that gravity has no effect on settling them but they, instead, stay in suspension. 

Fiiedlander (1960), Hunt (1980), Filella and Buffle (1993), and others have analyzed the effect of colloid agglomeration by coagulation and particle removal by settling on the shape of the particle size distribution function as expressed by equation 4. The predictions of model calculations are often consistent with the range of values of /3 observed in aquatic systems. 

For complex fluids, the gap in the spatio-temporal scales between the smallest microstructures and the largest structures is much smaller than for simple fluids. Dzwinel and Yuen (2000b) have shown that by using moderate number of particles, we can simulate in two dimensions multiresolution structures ranging frommicellar arrays to the large colloidal agglomerates. 

Mesocopic flows are important to understand because they hold the key to the interaction between the macroscopic flow and the microstructural inhomogeneities. This is especially true in colloidal flows, which involve colloidal mixtures, thermal fluctuations and particle-particle interactions. Dynamic processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale, this... 

Bitea, C. et al.. Time-resolved observation of ZrOj-colloid agglomeration. Colloids Surf. A, 215, 55,2003. 

The main common characteristic of colloidal particles is their small size (typically 1 to 10 nm). The size of nanopartides in solution is dynamic and continuous redistribution in size can occur. In most cases, agglomeration leads to the formation of less active larger metal partides and this process may end in predpitation of larger crystals (palladium black). The per-atom catalytic efSdency of metal par-tides increases as the partide size decreases however, the probability of colloid agglomeration increases as their size decreases. To prevent agglomeration (and aggregation), and to preserve the finely dispersed state of the original partides, colloids are often prepared in the presence of stabilizers that adsorb onto the partide surface. 

Similarly as the processes of coagulation and break-up characterized for mixtures of fluids, the processes of micelles crystallization, colloidal agglomeration, and process of dispersion occurring in colloidal suspensions, can be simulated by using multilevel particle models described in Section ll.E. This time, however, solid fraction, colloidal beads, has to be simulated by using different interaction paradigm. 

FIGURE 26.28 (a) Micellar structures obtained by using MD-DPD simulations (above) and (below) comparison of the microstrucmres obtained from simulations (1) to real colloidal arrays (2). (b) The colloidal agglomerates simulated in increasing spatial scales. 

In Figure 26.30, we present the snapshots from 2-D and 3-D simulations of dispersion of colloidal agglomerate accelerated in a periodic box. We recognize several stages of granulation, which usually occur with some degree of overlap ... 

Dzwinel, W. and Yuen, D.A., Mesoscopic dispersion of colloidal agglomerate in complex fluid modeled by a hybrid fluid particle model, J. Coll. Inter. Set, 217, 463-480, 2002. 

The proposed mechanism of the hydrosilylation involves the formation of the metal colloid-RsSiH intermediate, followed by a nucleophilic attack of the olefin. The function of O2 predominantly is to prevent irreversible colloid agglomeration. 

Zeta potential is related to electrostatic repulsion when two colloids approach each other and their double layers begin to interfere. An electrostatic repulsion curve is used to indicate the energy that must be overcome if the particles are to be forced together. It has a maximum value when the particles are almost touching and decreases to zero outside the double layer. In the meantime there are the van der Waals attraction forces between the individual molecules in any colloid that pulls colloids together. These two opposite types of forces determine whether colloids agglomerate or remain dispersed. If the net energy... 

Zeta potential test is the measurement of the attraction-repulsion forces (charges) between particles when they are dispersed in a liquid. It gives information about the dispersion mechanism, stability of the colloids, agglomerates, etc., and especially, about the electrostatic processes. There are some types of equipment which are focused on the analysis of nanomaterials, and with which it is possible to measure the zeta potential and also the particle size in liquid dispersion. 

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