DIRECT MICROSCOPIC STUDIES OF PARTICLE MOTION IN STABLE DISPERSIONS AND IN FLOCCULES

An apparatus has been constructed for the direct microscopic examination of colloidal particles which when coupled with a high-speed cine-camera allowed observations on particle motion to be made. The coordinates of the particle as a function of time were then obtained by projecting the film on to a digitizing table. The basic procedure was tested by measuring the diffusion coefficients of spherical polystyrene particles with diameters of 0.916, 2.00, and 3.76 μm and good agreement was found between experiment and theory. The technique was then used to examine aggregates formed by the addition of electrolyte. Evidence was obtained for a steady state in the kinetics of flocculation, a finite life-time in the associated state for doublets before dissociating into single particles, and for the mobility of particles within floccules. © 1979.