Aggregation of colloidal particles

Macrogelation proceeds by a mechanism completely different to that described by mean-field models (Chapter 3). In fact, it resembles the chemical aggregation of colloidal particles. At higher conversions the void space containing monomers is filled in by polymerization, so that the high-conversion structure appears to be less inhomogeneous than the structure at the gel point however, permanent inhomogeneities still persist. 

When boiled, the violet solution becomes blue, attributable, perhaps, to aggregation of colloidal particles. 

The reverse of the coagulation process is peptization. It is well known from analytical chemistry that fresh precipitates are easier to disperse than old ones, which indicates qualitatively that an aggregate of colloidal particles is not in equillibrium and that irreversible, time-dependent processes occur in coagulation. As pointed out Frens and Overbeek (1971) the interpretation of peptization phenomena with aggregated systems is not possible unless the data are obtained in experiments with a shorter time scale than the aging time of the aggregate. They demonstrated that it was possible to follow the kinetics of peptization by suddenly diluting the sol... 

The basic theoretical approach for the analysis of diffusion controlled reactions is due to Smoluchowski [9] who developed it for the analysis of diffusion limited aggregation of colloidal particles. We discuss the generalization of this approach to the case of rodlike molecules here. The computational method best suited for the simulation of the polymerization of rodlike molecules is Brownian dynamics. We discuss in this review both multiparticle Brownian dynamics and pairwise Brownian dynamics the latter is a hybrid method combining Smoluchowski s [9] theory and Brownian... 

Agglomeration A combination or aggregation of colloidal particles suspended in a liquid into clusters of approximately spherical shape. Aggregate A compounding ingredient generally used to reduce the cost of materials. 

To improve the physical structure of the compost by causing aggregation of colloidal particles. This produces a more granular, open structure which results in larger air spaces and improved aeration. 

Consequently, synthetic hydrophilic polymers such as polyvinyl alcohol, and polyvinylpyrrolidone, and polyvinylmethyl ester are interesting for two reasons i.e. (1) they coordinate with metal ions thereby decreasing the rate of metal reduction, and (2) they prevent aggregation of colloidal particles. The simplicity of preparation of colloidal metal dispersions, the feasibility of controlling particle sizes, and some other advantages place these polymers as promising catalytic systems [32,53, S3 a]. 

Shamurina, M. V. Roldugin, V. I. Pryamova, T. D. Visotskii, V. V. Aggregation of colloidal particles in curing systems. Colloidal Journal, 1994,56(3), 451-454. Naphadzokova, L. Kh. Kozlov, G. V. Fractal Analysis and Synergetics of Catalysis in Nanosystems. Moscow, Publishers of Academy of Natural Sciences, 2009,230. Rammal, R. Toulouse, G. Random walks on fiactal structures and percolation clusters. J. Phys. Lett. (Paris), 1983,44(1), L13-L22. 

By a theory first developed by Fut hs it is possible, however, to obtain a more quantitative formulation of this criterion of stability. In this theory, the probability of aggregation of colloidal particles is treated as a diffusion problem, just as in the well known theory of rapid coagulation by Von Smoluchowski. ... 

Coagulum an aggregate of colloidal particles having a relatively tight, dense structure formed as a result of the inabihty of the colloidal system to... 

The study of the rates of aggregation of colloidal particles owing to Brownian motion has a long history and was initiated by von Smoluchowski in 1916. Several solutions to the Smoluchowski equation have been attempted since then and two will be sketched here. The problem is to establish the time evolution of the number and size of the agglomerates in terms of the number of monomer particles. The expressions are typical for simplified models as is usual in physical chemistry. 

Bouyer, F., Robben, A., Yu, W.L., and Borkovec, M. 2001. Aggregation of colloid particles in the presence of oppositely charged polyelectrolyte Effect of surface charge heterogeneities. Langmuir 17 5225-5231. 

Koltover I, Radler JO, Safinya CR (1999) Membrane mediated attraction and ordered aggregation of colloidal particles bound to giant phospholipid vesicles. Phys Rev Lett 82 1991-1994... 

The aggregation of colloidal particles is very important in a number of processes, including industrial processes and aquatic chemical phenomena. The ways in which colloidal particles of minerals come together and settle out of water are crucial in the formation of mineral deposits. The bacteria in colloidal suspensions that devour sewage in the water at a sewage treatment plant must eventually be brought out of colloidal suspension to obtain purified water. Crude oil frequently comes out of the ground as a colloidal suspension in water the colloidal particles of hydrocarbon must be separated from the water before the crude oil can be refined. 

OH are the charge-determining ions, and, hence, the colloidal stability is sensitive to the pH. By adjusting the pH, low C values for most of the materials may be reached so that aggregation readily occurs and the materials can be removed by sedimentation or filtration. In fact, for aggregation to occur, it would be most favorable if some components have a positive value for and others a negative. The aggregation of colloidal particles is discussed in more detail in Chapter 16. 

In the present case, a colloidal phase starts forming 7 h after the initiation of the reaction, which consists of nanoparticles suspended in the solution matrix. As a result of the self-aggregation of colloidal particles, solid-phase nucleation centers form with dendritic structure. These colloidal particles have been found to self-aggregate and exhibit nucleation centers of dendritic character. Earlier formed nuclei are more in number than those formed later and participated extensively in nucleation process. 

Consider, for instance, the aggregation of colloidal particles at 1 ppmw and at 1 wt% for identical bulk and interfacial properties. The corresponding rates of aggregation J then differ by a factor of 10. ... 

Self-similar behavior has also been observed in computer simulation of aggregation processes. Thus aggregates of colloidal particles in diffusion-limited aggregation processes have been found to display self-similar behavior (Meakin, 1983). 

The effect of hydrodynamic interactions on aggregation of colloidal particles may be rather essential and simulation results show that they constrain the growth of aggregates [63]. Computational simulation predicts that many-body hydrodynamic interactions between colloidal particle are able to reduce the sohd fraction required for percolation or gelation [64, 65]. The merging of clusters into condensed aggregate was observed at particle volume fracture p as low as 0.06-0.12 [64]. 

Aggregation of colloidal particles has been studied since the middle of the 19th century, with important works such as those of Faraday s studies of aggregating gold particles. The first theoretical attempts to model aggregation were made by M. von Smoluchowski his theories treat the initial stage where only particle doublets are formed. 

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