Polymers charge patch neutralization

As mentioned earlier, polymers can exert a dramatic influence on colloidal stability. However, the description of particle interactions in the presence of polymers is complex, and even a qualitative estimation of conditions for attraction or repulsion has yet to be developed. Three theories have been proposed to explain flocculation of charged particles by oppositely charged polyelectrolytes bridging, simple charge neutralization, and charge patch neutralization. 

Simple Charge Neutralization and Charge Patch Neutralization Oppositely charged polyelectrolytes reduce the particle surface charge density such that particles may approach each other sufficiently closely so that the attractive van der Waals force becomes effective. Flocculation caused by this mechanism should not be sensitive to the molecular weight of the polymer. 

In the cases of aggregation by charge patch neutralization or bridging, it is necessary to include steric or bridging forces. Bridging flocculation takes place when polymer chains adsorb on more than one particle and act as bridges. Invoking... 

A characteristic difference between charge neutralization and patching is that the rate of coagulation for the former mechanism increases with electrolyte concentration. Once an optimal electrolyte concentration has been attained, however, the rate of flocculation by patching will decrease with electrolyte content due to the fact that the electrolyte cations will force the polymer from the particle surface. 

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