Half suspension flocculation

Flocculation is a kinetic process and the rate at which a colloidal suspension flocculates forms one of its most important characteristics. Smoluchowski (1917) distinguished between rapid flocculation and slow flocculation and developed a theory based on the rate of collision between the particles (2). Rapid flocculation is considered to take place in the absence of a potential barrier and is limited only by the rate of diffusion of the particles towards one another. The flocculation time, defined as the time tia required for the number of particles to be reduced by one-half of the initial value is given by... 

The result of these combined static and d)mamic depletion effects is an effective lubricating layer at the wall. This can be modelled simply as a particle-free layer of about half a particle-radius wide. Hence the lubricating effect is larger for larger particles, and in this context large particles include floes, so that at low shear rates, slip effects are stronger than at higher shear rates for flocculated suspensions. 

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