Flocculation colloid stability

Polymer adsorption is important in the flocculation and stabilization of colloidal sols and has been reviewed by Vincent et al. (1) and Tadros (2). Polyvinyl alcohol (PVA) has been used in these studies because of its practical application in textiles, adhesives, and coatings. The adsorption of PVA has been studied on silver iodide by Fleer (3) and Koopal (4), and on polystyrene (PS) latex particles by Garvey (5). The adsorption isotherms reported by these workers extend up to 600 ppm PVA. The adsorption at... 

Attempts to measure a critical flocculation volume of nonsolvent by titration with non-solvent as used by Napper (4) were not successful. A sharp transition between a relatively stable dispersion and a sudden loss of all colloidal stability was never observed and no unambiguous end-points could be detected. 

Lyklema, J. (1985), "How Polymers Adsorb and Affect Colloid Stability, Flocculation, Sedimentation, and Consolidation" Proceedings of the Engineering Foundation Conference, Sea Island, Georgia, in B. M. Moudgil and P. Somasundaran, Eds., pp. 3-21. 

The well-known DLVO theory of colloid stability (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the liquid—solid interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobility or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see COLLOIDS). 

Experiments on interactions of polysaccharides with casein micelles show similar trends to those with casein-coated droplets. For example, Maroziene and de Kruif (2000) demonstrated the pH-reversible adsorption of pectin molecules onto casein micelles at pH = 5.3, with bridging flocculation of casein micelles observed at low polysaccharide concentrations. In turn, Tromp et al. (2004) have found that complexes of casein micelles with adsorbed high-methoxy pectin (DE = 72.2%) form a self-supporting network which can provide colloidal stability in acidified milk drinks. It was inferred that non-adsorbed pectin in the serum was linked to this network owing to the absence of mobility of all the pectin in the micellar casein dispersion. Hence it seems that the presence of non-adsorbed pectin is not needed to maintain stability of an acid milk drink system. It was stated by Tromp et al. (2004) that the adsorption of pectin was irreversible in practical terms, i.e., the polysaccharide did not desorb under the influence of thermal motion. 

In general, A and B subchains in an AB- or an ABA-type block copolymer have different solubilities or affinities for a solvent or other polymers. Therefore, it is expected that a block copolymer is surface-active when dissolved in a suitable solvent or mixed in polymer melts108. This property of block copolymers is now utilized to stabilize or flocculate colloidal dispersions. Blocks A, which are insoluble in a given solvent, are anchored in an insoluble polymer particle, and blocks B, which are soluble in the solvent, form a surface layer around the particle. 

GREGORY, J., Effects of polymers on colloid stability , in Scientific Basis of Flocculation (see reference 100), pp. 101-130... 

In the previous sections we have considered various ways of achieving the colloid stability of polymer latices and also of obtaining instability, i.e. either coagulation or flocculation. 

The principles of colloid stability, including DLVO theory, disjoining pressure, the Marangoni effect, surface viscosity, and steric stabilization, can be usefully applied to many food systems [291,293], Walstra [291] provides some examples of DLVO calculations, steric stabilization and bridging flocculation for food colloid systems. 

Adhesive interaction of one particle toward another surface is closely related to the various phenomena associated with colloid chemistry such as colloidal stability, suspension, flocculation, and so forth. For instance, solid particles in water are maintained in suspension, in other words, they may be protected against flocculation due to the van der Waals attraction, if their surfaces possess electrical charging or some protective substances such as hydrophilic... 

In addition to the components given above (v0> v> C0) controlling colloidal flocculation or stability (stability is defined as the state or the conditions under which primary colloids are maintained) (Schofield and Samson, 1954 Shainberg and Letey,... 

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