| The addition of polymer to suspensions of collidal particles is mainly relate to two process: stabilization and flocculation. Compared with the coagulation of electrolytes, flocculation has a lot of advantages, especially for the suspensions of large sizes particles,such as fast and high efficiency flocculation, the less demanded amount of flocculant and so on. Therefore, flocculatin is an important part of many technical processes. Typical examples are wastewater treatment and sludge dewatering, pulp and paper production and the pharmaceutical, cosmetics, as well as metal- working industries. The stabilization effect of polymers chiefly refer to the polymers, which are adsorbed on the surface of colloidal particles, forming a layer of polymer and providing protective function, in order to avoid particles flocculation. Then the process of adsorption is usually through hydrogen bonding and van der Waals force. For example, in the suspensions of silica colloidal particles and PEG, the polymer can absorb on the surface of silica particles through the hydrogen bonding between -CH2-CH2-O- and Si-OH. Researchers have proposed steric stabilization theory and depletion stabilization theory to explain the stabilization effect of polymers. The first theory is put forward when the polymers are adsored and the colloidal particles with polymers layer close enough, the adsorbed polymer layers due to loss of structural entropy can result repulsive potential or the adsorption layers are compressed to produce elastic repulsive potential. So the additional repulsive potential energy can improve the collidal stability. The second theory is proposed when the polymers are negative adsorption. The adjacent colloidal particles are moving close and the polymers will move to the bulk solution, so this process will consume more power and therefore can prevent particles flocculation.At present, the extremely extensive application of polymer flocculants is mainly polyelectrolytes, such as polyacrylamide and its partially hydrolyzed products, polyacrylic acid, polystyrene sulfonate and so on. The flocculation process is determined by several different parameters:molecular weight and charge density of the polyelectrolytes, ionic strength of the solution, size and surface charge of the dispersed particles as well as mixing method and intensity. These parameters chiefly determine the conformation of the adsorbed polyelectrolytes and the charges of the polyelectrolyte-covered particles, which have a key influence on the flocculation behavior of the suspension.In this thesis, we selected sodium polystyrene sulfonate, mainly because Poly(styreneslfonic acid) is strongly acidic and therefore remains fully dissociated in typical pH ranges(i.e.,l-14). We successfully synthesized PSSNa homopolymers and PSSNa-b-PEG-b-PSSNa block copolymers via atom transfer radical polymerization (ATRP) in water and methanol. And then the measurement of FT-IR, NMR and GPC have proved the structure and the PDI is less than 1.5.The flocculation process is often described by a simple model, distinguishing between bridging and charge neutralization. Because the molecular weight of the PSSNa is small, charge neutralization may play a significant role in the process of flocculation, which is proved by the measurement of Zeta potential, and turbidity test.The flexible hydrophilic PEG segments in the chain of PSSNa are beneficial PSSNa molecular chain stretching, but the stabilizing effect of PEG is more competitive when the molecular weight is 10000g/mol. So finally the flocculation efficiency of the PSSNa-b-PEG-b- PSSNa block copolymers is decreased and the flocculation window becomes narrow.
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