Mixing of disperse systems (particles and powders) is a traditional unit operation of process engineering which is of central importance in various technological areas. Applications of mixed particulate systems range from processing of food, pharmaceutical and chemical substances to material processing and materials engineering. Functional mixing of different particle types (hetero-aggregation) has the potential of creating outstanding new properties of dispersed products, which depend on the mixture composition (e.g. number of components, concentration, total quantity) and on various secondary process conditions (e.g. agglomeration, coating).
In this context, a new product property can emerge from the direct contact of different particles (hetero-contact) and thus by the resulting interface between the respective particular components. Many applications have shown that these hetero-contacts are of fundamental importance for specific functional properties. In most cases the new properties result from the transfer of charges, mass, heat, forces, or moments without the need of a chemical reaction of its components. Thus, the quality of such a particulate mixture is directly linked to the contact points and interfaces of different particles and the details of the interaction between its species in contact.
The new property from the contact zone controls the material and product properties of the entire system that is named hetero-contact in the context of the Priority Programme. Direct information about hetero-contact quality (e.g. number of contacts, transport properties between different particle types) could therefore be the base for a fundamental description of the new properties of the particle mixture (quality of the mixture and material function). At the same time, the hetero-aggregation process for creating of such hetero-contacts needs to be investigated and controlled.