Flocculation mechanism

Particle formation in the early stages of a batch reaction is normally quite rapid. Hence the particle surface area produced is able to adsorb the free emulsifier quite early in the reaction (2 to 10% conversion) and particle formation ceases, or at best slows to a very low rate. Particles formed in the beginning of the reaction would have approximately identical ages at the end of the batch reaction. These particles would be expected to be nearly the same size unless flocculation mechanisms, stochostic differences, or secondary nucleation factors are significant. 

Yeast flocculation mechanism can be described as a phenomenon of adhesion to certain surfaces. The ability to adhere to surfaces and to form biofilm is the basis of the pathogenicity of Candida species. Pathogens adhere to mucous membranes and wounds, they stick to medical instruments and prosthesis, and thus contaminate surfaces in food processing facilities. The high mortality rate in disseminated fungal infections caused an increase in the amount of research on the molecular basis of the adhesive phenomena in Candida. This research discovered a considerable overlap in the molecular regulation of all forms of adhesive behavior. ... 

If the von Smoluchowski rate law (Eq. 6.10) is to be consistent with the formation of cluster fractals, then it must in some way also exhibit scaling properties. These properties, in turn, have to be exhibited by its second-order rate coefficient kmn since this parameter represents the flocculation mechanism, aside from the binary-encounter feature implicit in the sequential reaction in Eq. 6.8. The model expression for kmn in Eq. 6.16b, for example, should have a scaling property. Indeed, if the assumption is made that DJRm (m = 1, 2,. . . ) is constant, Eq. 6.16c applies, and if cluster fractals are formed, Eq. 6.1 can be used (with R replacing L) to put Eq. 6.16c into the form... 

Clay colloids are irregular in shape and their charges are separated into planar charges and edge charges. Because of this charge distribution, two unique flocculation mechanisms are encountered. One is phase to phase flocculation, commonly encoun-... 

It is well known that the presence of an excess of nonadsorbed polymer can result in flocculation of colloidal particles by the so-called depletion flocculation mechanism [13], In the clay-PEO system, the excess PEO molecules in the supernatant fluid would exert an osmotic pressure on the gel, and the effect should be similar to that of applying an external pressure to the gel indeed, because the... 

FIGURE 7.17 Schematic representation of hypothesized phase separation flocculation mechanism. 

For significant improvement in supernatant clarity obtained in the scheme when the pH was shifted rather than fixed, the following two-step flocculation mechanism is proposed ... 

Starch-induced flocculation of 1% (w/w) kaolin suspensions and the adsorption of NaCMC were investigated by Jamstrom et al., where the kaolin was partly pretreated with sodium polyacrylate of low molecular weight (PAA) [22], In all flocculation experiments the kaolin suspension as well as the starch solution were adjusted to pH 7.5. The flocculation behavior of the PAA-treated suspension indicated that depletion flocculation is a very likely flocculation mechanism. When a hydrophobically modified starch was added, no flocculation occurred, and no adsorption of the modified starch on the kaolin particles could be detected. It is reasonable that water is a less good solvent for the hydrophobically modified starch and thus may cause the impossibility of depletion flocculation. On the other hand, a dispersing... 

Figure 11,44, Proposed flocculated mechanism. [Reproduced from ref. 89 with kind permission of Huthig Wepf Publishers.]...

Fig. 10.3. Diagram of the flocculation mechanism of proteins in wine dnring fining (Riberean-Gayon et al, 1977)...

From their results, Andersson and Lindgren concluded that for both the cationic starch-ACS and CPAM-ACS systems the main flocculation mechanisms were electrostatic interactions, for example, charge neutralization and bridging. 

Figure 7.14. Sequence showing schematically (a) charge-stabilized particles, (b) particles flocculated by the patch flocculation mechanism, and (c) particles restabilized by steric repulsive (chain overlap) interactions at higher levels of polymer surface coverage...

The influence of charge and molar mass on the flocculation mechanism was also confirmed by results obtained for water treatment, where the influence of humic acid on the flocculation of clay was investigated [26]. The separation of clay particles was influenced by the presence of humic compounds, which act like an additional PA in the clay dispersion. Owing to their adsorption on clay and the higher anionic charge... 

---