Stability Measurement—Aspects of Data Interpretation

The fact that the origin and mechanisms of particle aggregation are principally understood and can even be quantitatively predicted by means of aggregation kernels and stability ratio (cf. Sect. 5.2.3) does not imply that such a prediction is easy to accomplish or that the interfacial properties can be easily derived from stability measurements. Indeed, the stability theory ignores the origin of interparticle forces and is indifferent towards their temporal evolutions. If, however. 

Stability measurements are evaluated with regard to the prevailing microprocesses, these aspects cannot be ignored. A profound stability analysis should, therefore, explore  

In stability measurements, the particle concentration may vary between a few ppm and several percents (by weight). The former values are relevant, for example, when investigating the behaviour of colloidal particles in environmental media or physiological solutions. The latter typically occur when colloids are used as main product components (e.g. pigments) or as fillers. Since the aggregation rate J is proportional to the squared particle concentration (Eq. 5.29) such concentration differences have dramatic effects on the observed suspensions stability. 

Consider, for instance, the aggregation of colloidal particles at 1 ppmw and at 1 wt% for identical bulk and interfacial properties. The corresponding rates of aggregation J then differ by a factor of 10.  

The third aspect, homo- and/or heteroaggregation, concerns the homogeneity of the evolving aggregates. Only a few colloidal suspensions with industrial relevance contain just one particulate phase (e.g. CMP slurries) more typical are products that are composed of several dispersed phases (e.g. ceramic slurries, paints, or food products). Therefore, distinction should be made between the aggregation of different components (heteroaggregation) and that within one dispersed phase (homo-aggregation). 

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