In the dispersed state, the particles are separate and move erratically with Brownian motion, whereas the flocced state corresponds to particles which clump together in aggregates under the influence of attractive interparticle forces. A new experiment showed that this view is too simple because even the most dispersed colloids are found to contain large aggregates in apparent equilibrium with the dispersed particles. These new aggregates have been termed multiplets to distinguish them from the doublets, triplets etc of particles formed sequentially by normal flocculation processes. It is suggested that these multiplets are caused by small adhesion between the particles which leads to phase separation of nuclei of aggregated particles with low tendency to dissolve or grow. According to this novel argument, dispersions exist in a two-phase state containing both primary particles and multiplets.
Flocculation occurs when the multiplet volume increases rapidly.
Introduction A colloid is a mix of fine particles in a fluid. When the particles do not stick together, they remain separate and move like atoms with Brownian motion, causing the mix to behave in a perfectly fluid way. This is the dispersed state typified by silica sol or by blood. This is the flocculated or gelled state. It has been thought that fully dispersed colloids, although technically metastable, can remain in the dispersed state for ever, as witnessed by the gold sols made by Faraday and still dispersed after one hundred and forty years at the Royal Institution.