Dispersing polymers, anionic charge

The absolute value of the zeta potential decreases until a plateau is reached at a certain polyanion concentration. A contrary effect is obtained in the case of adding a polycation. A partial stabilization of the kaolin particles can be realized due to an adsorption of anionic charged macromolecules at the edges of the kaolin platelets. By adding a polycation to the kaolin dispersion, an adsorption at the negative basal surface becomes possible, and the iep of the particles is reached very quickly at low PEI concentrations. A further addition of PEI leads to an increase of the zeta potential while flocculation was observed. This is because the adsorption of cationic polymer can cause a face-to-face association that can generate polymer-kaolin complexes. 

The development of micro-particle retention systems radically changes the chemistry. In these systems an overdose of cationic material is added to the thin stock, such that the system becomes cationically dispersed. An anionic micro-particle is later added to flocculate the stock. Under these circumstances a complete starch cook out may not be necessary - especially if the system is being over-charged with a polymer rather than starch. Cross-linked cationic starches that do not fully disperse may be used in such systems. The partially dispersed starch acts partly as a colloid and partly as a particle, having a larger active radius than a fully dispersed starch molecule. Benefits in starch retention are claimed. 

PSCs can be also used as flocculants in montmorrilonite dispersions [128]. An anionic surfactant (SDS) was combined with a cationic polymer (PDADMAC). At a 1 1 molar ratio, optimal flocculation was obtained owing to the formation of an insoluble surfactant-polymer complex in the presence of particles. Such interactions may lead to a flocculation mechanism that combines polymer adsorption, charge neutralization, and hydrophobic interactions. Other experiments have shown that a similar flocculation process can be achieved by using a cationic surfactant and anionic polymer [127]. 

Commercial aqueous dispersions of FEP are supplied with 54 to 55% by weight of hydrophobic negatively charged particles with the addition of approximately 6% by weight of a mixture of nonionic and anionic surfactants based on polymer content. The particle size range is 0.1 to 0.26 pm. Nominal pH of the dispersion is 9.5 and the viscosity at room temperature is approximately 25 cP.6... 

---