The energy barrier against colloid aggregation depends Perikinetic and orthokinetic aggregation in laminar tube flow on the surface charge density of the latex and the range of of hydrophilic polystyrene latex particles was investigated to deterthe electrical interactions in the suspending liquid phase. mine the aggregation characteristics of weakly unstable colloids The correlation with the retardation in aggregation kinetics in aqueous media. The weight S and number N average sizes of has been established by Fuchs ( 17). An equivalent correlacolloids and the colloid mass frequency c(n) were determined by tion between the aggregation kinetics and the intrinsic reacparticle counting. Destabilization of hydrated latex particles was tivity of the colloids has been established by numerical simufound to be predicted by DLVO theories as far as the repulsive lation of the reaction-limited process (18). The success of forces of the hydration layer were assumed to oppose the van der Smoluchowski's kinetic theory and numerical studies is Waals attractive forces, the combined effects being expressed using based on the cancellation of omissions of hydrodynamic and an apparent low Hamaker constant. Deviation from the usual reaction-limited aggregation process could be established by com-van der Waals forces. Including viscous interactions together paring experimental and theoretical power laws for perikinetic with van der Waals attraction, but excluding double layer processes. The development of orthokinetic processes depended repulsion leads to values of the perikinetic aggregation effion latex concentration and shear rate. At a given mean shear rate ciency that are of the order of unity and that are very insensiof 106 s 01 the aggregation rate increased with the latex concentrative to the value of the Hamaker constant. A twenty-fold tion below 0.3 g/L, while above this concentration the mass of change in the Hamaker constant induces only a negligible aggregates collected at the tube exit strongly decreased. Hydrodychange in the aggregation efficiency. However, cancellation namic interactions similarly modified the collision efficiency of the may no longer be valid when electrical and hydration forces smallest colloids, whereas the volume flow rate slightly modified oppose close contact. The present work aimed to determine the mass distribution of aggregates of intermediate and large sizes. the influence of hydration forces on the aggregation kinetics The true collision efficiency in laminar tube flow could be estaband structural characteristics of weakly destabilized colloids lished by taking into account the effective volume fraction of agaggregating under peri-and orthokinetic conditions. We ingregates. α§ 1998 Academic Press vestigated the kinetics of aggregation by determining the Key Words: aggregation of hydrophilic colloids; aggregation in laminar tube flow; collision efficiency of aggregates of unequal variation with time of the number N(t) and weight S(t) sizes.
average masses of the colloids and the structural characteristics of the suspension by determining the mass frequency and fractal dimension of the colloids. 1 To whom correspondence should be addressed. namic interactions between colliding particles (11, 12). 1