Heteroflocculation by asymmetric polymer bridging

Heteroflocculation by polymer bridging can lead to behavior that is qualitatively different from homoflocculation, Heteroflocculation between two different particles can occur, even when the (freely dissolved) polymer does not adsorb on one of the two particles, The polymer can first adsorb on the surface of one particle, which modifies the configurations and thus the entropy of the polymer, and subsequently on the surface of the other particle, thus causing bridging. This type of asymmetric polymer bridging does not lead to steric stability at excess polymer concentrations, This behavior was observed for the heteroflocculation of clay particles with pulp fibers induced by polyethylene oxide (PEG). An additional interesting feature of this system is that heteroflocculation is only transient, apparently due to rearrangement and flattening of the PEO molecules adsorbed on the clay surface, which causes the clay particles to leave the fibers. The rearrangement time increases strongly with the fractional coverage of PEO on clay, Thus, in principle, transient heteroflocculation can be used to measure the rearrangement time as a function of polymer coverage on the surface. (C) 1996 Academic Press, Inc.