Abstract
Flocculation of a monodisperse polystyrene latex by the addition of sodium polyacrylate (SPA) is studied by bulk observation and in situ observation of the particles by an optical microscope. The results of the bulk observation, namely, the apparent feature of flocculation produced by various amount of SPA added, are in accordance with knowledge now widely known, except that in the presence of certain amounts of SPA the subsided sediment and the wall of the vessel are tinted with iridescence. But the results of the microscopic observation are rather striking; (1) the particles in each floc are arranged in highly regular hexagonal arrays, (2) the flocs (preferably called crystallites) grow and finally attain an equilibrium state with the environment, (3) nucleation, segregation and so forth are observed. These processes are reversible; namely, by shaking the vessel, the flocs are decomposed into a dispersion of single particles and upon quiet standing form again. The behavior of the particles closely resembles what we picture about the growth of real crystals (of atoms or molecules) from vapor.
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