Aggregate structure and strength

In previous sections, strong irreversible aggregation (coagulation) and weak, reversible aggregation (flocculation) have been discussed, and some aspects of aggregate structure 

Alternatively, if the hydrodynamic diameter (%) of the aggregates is measured, using dynamic light scattering, as a function of time (t), then, under certain conditions, (Asnaghi etal, 1992) the following relationship holds  

For weak, reversible flocculation, values of df 2 are often observed in addition, some time dependence may also be observed. This is because singlet particles can break away, and return to the floe in a more favourable (i.e. a lower potential energy) position. Clearly, if a colloidal crystal is achieved, df approaches the maximum value of 3. 

The critical flocculation temperature (CFT), below which the microgel particles are (thermodynamically) stable, is 34°C. Just beyond 34 C df is 2.0, indicative of weak, reversible 

A number of more classical studies on latex particle assemblies have been reported in the past, using pressure-cell equipment. For example, Cairns etal. (1976) used this method to study the interaction of PMMA particles with grafted PHS chains, that is, a similar system to Pusey and van Megen s, discussed earlier, but with dodecane as the solvent. Napper (1983) has discussed how pair-potentials might be extracted from pressure/volume fraction data obtained using this method. 

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