The main technical goals and development areas of the priority programs are
- the development of sophisticated methods for the characterization of hetero-aggregates in disperse systems,
- the development of suitable process diagnostics that feature component-specific detection,
- the derivation of proper process descriptions and simulations with validated models (particle, continuum and/or population based) for mixtures of <1 µm sized particle systems, and
- the establishment of efficient model couplings (for example DEM-CFD) for the ab-initio gas phase process design.
These goals aim to a fundamental understanding of the relevant mixing phenomena on length scales in the sub-micrometre range and their modelling as well as transfer into applications of tailored hetero-aggregated particulate systems and aggregation processes.
The processes for designing hetero-aggregates are divided into the formulation (from existing particle systems) and the production (from molecules and their reaction products) of the hetero-aggregates. The solely focus of the programme is on processes in the gas phase, where both adhesion forces and specific charge distributions of particles play an important role. Gas-phase aggregation processes can be implemented with different methods and reactor concepts.
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 (for example number of components, concentration, total quantity) and on various secondary process conditions (for example 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 (for example 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.
In the first three years of SPP 2289, the recursive approach dominates, adapting the material system of heteroaggregates to the process measurement technique and the characterisation methods of heteroaggregates and their populations. Special focus is:
- on the establishment of aerosol processes for the defined generation of heteroaggregates, which can also be adapted to process diagnostics for the detection of mixing processes < 1 μm,
- the derivation of particulate sample trains from fast aggregation processes, the establishment of tomographic methods for the characterisation of heteroaggregates with sizes < 1 μm and - their mathematical basis for the description of heteroaggregates as well as
- the establishment of process models and simulations that cover mixing lengths <1 μm.