Agglomeration and Aggregation of Nanoparticles

Agglomeration of nanoparticles is an often-observed phenomenon. In severe cases, it may lead to a reduction in the usability of a product. Therefore, it is necessary to study the processes that lead to this undesirable phenomenon. Analyzing this phenomenon, one learns that it is necessary to distinguish between ‘hard’ agglomerates called aggregates and ‘soft’ agglomerates. Furthermore, one has to distinguish arrangements, where, potentially, each particle may collide with each other or arrangements, where collisions are possible only with the next neighbors. The first of these cases is observed in case of synthesis, whereas the second one is typical for particles stored in a box. For the analysis of thermodynamic stability, the entropy of the mixture is the appropriate parameter described by the Gibbs equation. In lack of sufficient data for possible materials, it was not possible to calculate the free enthalpy to give thermodynamical valid description of the stability of the agglomerates. Furthermore, this paper indicates theoretical problems waiting for great ideas.