Clustering of binary colloidal suspensions: Experiment

The stability of binary colloidal suspensions is examined and compared to that of particle-polymer systems. In particle-polymer systems, it is known that the addition of free polymers within a concentration range of polymers to a stabilized dispersion leads to flocculation. Similar to particle-polymer systems, we have observed that in binary colloidal suspensions, particles of the first kind can be induced to flocculate by the presence of particles of the second kind, within a certain range of concentration of the second kind of particles. Moreover, we have observed the growth of clusters of particles 1 at a later time in the initially restabilized regime. This slow growth of clusters in the initially restabilized suspensions is associated with the slowing of particle movement due to higher particle 2 concentrations. The aging phenomenon (growth of clusters) that occurs at high particle 2 concentrations clearly indicates that the seemingly restabilized suspension at high particle 2 concentrations is not due to thermodynamics, but to slow kinetics associated with slow particle movements at high densities. A similar aging phenomenon was observed with a particle-polymer (α-Al₂O₃/PAA) system in the seeming restabilization regime at high polymer concentrations.