Polymer induced fragmentation of colloiids: Mechanism and kinetics

Abstract

The particle counter technique is used for studying the rate of aggregate fragmentation induced by polymer adsorption. The influeces of the hydrodynamic forces during aggregation and the degree of surface coverage before fragmentation were investigated. We determined that a scalling law a(x) ℞ x ^λ described the rate of break-up a(x) of aggregates of size x. Values of gl equal to 0.65 and 0.90 characterized the process for aggregates formed with and without stirring respectively. The establishment of an adsorption equilibrium for facing surfaces of adhering colloids was achieved by a reptation process in the restricted interfacial zones. The time prior to the beginning of the fragmentation decreased with the degree of coverage of the starved surface at the time of aggregation. The polymer concentration of the fragmentation medium influenced the fragment size distribution, which was described by the scaling law φ(x)=xν. The exponent gn was found to be equal to −1.2 in concentrated polymer solutions and equal to −1.75 in the more diluted ones. The rate of fragmentation determined from the variations of the weight S(t) and number N(t) average sizes, was much slower than the rate of break-up calculated from the theory, indicating that fragmentation is retarded by a concomitant aggregation.