ELASTIC PERCOLATION IN SUSPENSIONS FLOCCULATED BY POLYMER BRIDGING

The dynamic viscoelasticity was measured for silica suspensions flocculated by polymer bridging. When the particle andpolymer concentrations exceed some critical values, the suspensions respond elastically to small deformations because a network structure of unbounded floes is formed over the system. The dispersed particle is compared to the site and the polymer bridge to the bond in the percolation concept. Boundaries for elastic percolation were determined in terms of the site and bond occupancy, and the effect of particle size on the percolation boundary was examined. The theoretical percolation threshold depends on the coordination number of the lattice. A simple cubic lattice was adopted to analyze the percolation process. For suspensions containing sufficient adsorbing polymer, the critical behavior can be characterized by the site percolation. The critical site occupancy is about 0.35, and the elasticity exponent is about 4 irrespective of particle size. However, the bond percolation process cannot be explained by the theory on the same lattice. The critical bond occupancy experimentally determined for elastic percolation of flocculated suspensions is lower than the theoretical prediction and varies with the particle size. In bridging flocculation, a polymer chain adsorbs onto two or more particles to bind them together whereas each bond is regarded as independently distributed in the theoretical calculation. A series of several bridges formed by one polymer chain is not broken down to noninteracting bonds; this may be responsible for the low value of critical bond occupancy. © 1990, American Chemical Society. All rights reserved.