Neutron scattering studies on FLOC structures

Silica aggregares flocculated by water soluble polymers are examined using small angle scattering. We determine the structure of these flocs; we study factors which determine the structure and can make hypotheses as to the mechanism of flocculation. We find two general families of floc structure. The first kind have a liquid-like structure. These structures are formed when the inter-particle repulsions are strong, but of short range, and the absorbed layer is thick enough to extend beyond the double layer. Then the particles may be re-arranged into the ordered structure which is observed. This is a general case for flocculation with nonionic or lightly charged polymers. At larger length scales the liquid-like structure appears to be organized into a tenuous structure. The second kind of structure is formed by kinetic aggregation; in this case the repulsions between particles are neutralized or screened, and self-similar objects with a fractal dimension of ca.2. are formed. This is the general case for flocculation by strongly charged polymers, ionic surfactants and salts.;We also discuss preliminary results on the structure of the absorbed polymer layer in a floc and make a measurement on the repulsive and attractive forces between particles in a floc.