Kinetics of Coagulation and Flocculation

Similarly, a weak repulsive steric interaction in combination with a strong van der Waals interaction will result in flocculation. The kinetics of coagulation and flocculation in the presence of a total interaction energy profile either electrostatic or steric is discussed next. 

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The present paper deals with kinetics of coagulation of Phthallylsulfathiazole stabilized xylene in water emulsion in the presence of some cationic detergents. Rate of flocculation, rate of coalescence and rate of creaming have been determined. To estimate the stability of the present systems their zeta potentials have been measured and stability factors calculated. Temperature effect on the system was also studied. 

There are two general theories of the stabUity of lyophobic coUoids, or, more precisely, two general mechanisms controlling the dispersion and flocculation of these coUoids. Both theories regard adsorption of dissolved species as a key process in stabilization. However, one theory is based on a consideration of ionic forces near the interface, whereas the other is based on steric forces. The two theories complement each other and are in no sense contradictory. In some systems, one mechanism may be predominant, and in others both mechanisms may operate simultaneously. The fundamental kinetic considerations common to both theories are based on Smoluchowski s classical theory of the coagulation of coUoids. 

Tphe kinetics of the protease-triggered clotting of blood and milk has been formulated in a number of recent publications from this laboratory (1,2,3). In milk clotting, the coagulation is initiated through the limited proteolysis of -casein, the milk protein component which normally protects the casein micelles from flocculation by calcium ions (4). Kappa-casein is a single polypeptide chain of 169 residues, the sequence... 

Chen, W. J., D. P. Lin, and 1. P. Hsu (1998). Contrihution of electrostatic interaction to the dynamic stability coefficient for coagulation-flocculation kinetics of beta-iron oxy-hydroxides in polyelectrolyte solutions. J. Chem. Eng. Japan. 31, 5, 722-733. 

Alkylpyridinium or ammonium halides constitute a group of cationic detergents with well known surface properties. The kinetics of emulsion breaking or in general coagulation, comprises flocculation and coalscence. It has been reported (1) that cations and anions at low concentrations retard the coalescence and association of dispersed phase of emulsions. 

The kinetic theory of fast irreversible coagulation was developed by von Smoluchowski. Later the theory was extended to the case of slow and reversible coagulation. In any case of coagulation (flocculation), the general set of kinetic equations reads... 

The predictions of different quantitative criteria for stability-instability transitions were investigated [461], having in mind that the oscillatory forces exhibit both maxima, which play the role of barriers to coagulation, and minima that could produce flocculation or coalescence in colloidal dispersions (emulsions, foams, suspensions). The interplay of the oscillatory force with the van der Waals surface force was taken into account. Two different kinetic criteria were considered, which give similar and physically reasonable results about the stability-instability transitions. Diagrams were constructed, which show the values of the micelle volume fraction, for which the oscillatory barriers can prevent the particles from coming into close contact, or for which a strong flocculation in the depletion minimum or a weak flocculation in the first oscillatory minimum could be observed [461]. 

It is now well established that most colloidal systems in aqueous media remain stable because of the cooperative effect between electric charges attached to the suspended particles and the counter-ions in the immediate environment around them. A suitable description of this electrical picture,therefore, must be included in the foundation for any thermodynamic or statistical mechanical analysis of such colloidal systems. One should also point out,however, that many problems of practical interest are concerned with irreversible processes taking place in the colloid, i.e. coagulation or flocculation, rheology, and electro-kinetic behavior. An understanding of these processes cannot be derived from equilibrium phenomena. Moreover, even a complete treatment of colloid equilibrium should not be based exclusively on electrostatic considerations but should also allow for short range forces, such as van der Waals attraction. 

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