Flocculation theoretical considerations

S.4. Critical flocculation particle volume fraction Theoretical considerations... 

Regulation of the physico-chemical properties of colloid dispersions by polyelectrolytes is of great interest from the theoretical and practical points of view [89]. A consideration of the peculiarities of absorption of polyelectrolytes on disperse particles can be of help to clarify some aspects of kinetics and mechanism of flocculation, elemental acts of flocculation, as well as to provide the se-... 

Theoretical models for the dieleetrie properties of heterogeneous mixtures [for instance, Eq. (20), or extensions of this model] are commonly applied in order to explain or predict the dieleetrie behavior also of emulsions (106, 158). However, in the present theories a homogeneous distribution of the dispersed phase is required. This requirement is rarely fulfilled in a real emulsion system where the inherent instability makes the emulsions go through different stages on the way towards complete phase separation. Proeesses like sedimentation, flocculation, and coalescence continuously alter the state of the system (Fig. 36). These processes also influence the dielectric properties (159—162). Thus, the dielectric properties of one given sample may vary considerably over a period of time (160), depending on the emulsion rate. 

The flocculation of the yeast affects the mass transfer rates and, thus, the rate of fermentation considerably through the change of the exposed surface area for mass transfer per unit mass of the micro-organism. The flocculation process has been investigated experimentally by many researchers however, the theoretical basis for understanding the flocculation process is severely lacking. 

Even simply for the purpose of classifying rheological behaviour, it is convenient to distinguish between flocculated and non-flocculated systems. This is because, firstly, the theoretical position is much more well developed as a function of oil volume fraction for dispersed (non-flocculated) systems than for flocculated ones, an4 secondly, the experimental behaviour of many emulsion systems can be interpreted most effectively at the mechanistic level from a detailed consideration of the type and extent of flocculation. Much of the experimental work published recently on emulsion rheology has been concerned with the role of water-soluble polymers in controlling the structure and stability of flocculated systems. Of particular importance in such systems is the viscoelasticity of the polymer-containing aqueous continuous phase and the nature of the interaction between polymer and emulsion droplets. 

---