Polymer-induced flocculation, methods

A floe is a reversible aggregation of dispersed particles and can be easily filtered out of the solution. An alternative method for inducing flocculation involves adding polymers to the solution. This process works by taking advantage of the depletion forces discussed previously in this chapter. 

Another method of reducing creaming or sedimentation is to induce weak flocculation in the emulsion system. This may be achieved by controlling some parameters of the system, such as electrolyte concentration, adsorbed layer thickness and droplet size. These weakly flocculated emulsions are discussed in the next section. Alternatively, weak flocculation may be produced by addition of a free (non-adsorbing) polymer. Above a critical concentration of the added polymer, polymer-polymer interaction becomes favourable as a result of polymer coil overlap and the polymer chains are squeezed out from between the droplets. This results in a polymer-free zone between the droplets, and weak attraction occurs as a result of the higher osmotic pressure of the polymer solution outside the droplets. This phenomenon is usually referred to as depletion flocculation [59] and can be applied for structuring emulsions and hence reduction of creaming or sedimentation. 

Another method of reducing sedimentation is to employ the principle of depletion flocculation (described in Chapter 7). The addition of free (non-adsorbing) polymer can induce weak flocculation of the suspension, when the concentration or volume fraction of the free polymer ( p) exceeds a critical value denoted by p. Asakura and Oosawa reported the first quantitative analysis of the phenomenon [96]. They showed that when two particles approach to a separation that is smaller than the diameter of the free coil, polymer molecules are excluded from the interstices between the particles, leading to the formation a polymer-free zone (depletion zone). Figure 14.16 shows this for the situation below and above. ... 

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