FLOCCULATION OF SOLS OF POLYSILICIC ACID BY POLY(N,N-DIMETHYLAMINOETHYLMETHACRYLATE)

Flocculation of colloidal silica (SiO2) by poly(N,N-dimethylaminoethyl methacrylate) (PEMA) and the structure of the formed flocs were studi ed using sedimentation and quasi-elastic light scattering techniques. Floc was shown to consists of silica particles covered by the adsorbed polycation molecules. The gaps between sol particles are filled with water in which unbound polymeric segments - loops and tails - are diss olved. The floc represents highly swollen and weakly cross-linked PEMA network filled with SiO2 particles. The salt linkages between PEMA un its and surface silanol groups, which stabilize the colloid-polyelectr olyte complex, act as cross-links of three-dimentional network. Flocs are formed due to aggregation of the macromolecules adsorbed on the su rface of colloidal particles. Adsorption of the macromolecular segment s on the surface of the colloidal particles leads to considerable impo verishment of conformational set of macromolecules. Thus, the water, b eing a good solvent for the free polymer molecules, turns a poor solve nt for the polymeric chains adsorbed on the particles. As a result, th e polymer separates into the concentrated microphase, carrying the pol ymer-bound sol particles along into this phase.