The aim of this laboratory is the development of methodologies with which the processing problems of non-Newtonian fluids (i.e. fluids with complex flow behaviour) can be addressed rationally. A large number of industrially relevant materials belongs to this category. Concentrated colloidal suspensions and polymeric fluids (melts and solutions) consitute the two major classes of rheologically complex materials. Both are being studies here. Recently work has also started on surfactants. The analysis or simulation of a processing operation requires a suitable characterization of the materials used. Therefore rheological constitutive equations are being developed both for polymers and suspensions. In addition the experimental determination of rheological characteristics in complex fluids is studied extensively. As such fluids exhibit a variable, flow- induced, microstructure, the rheological measurements are supplemented with techniques that probe the changing structure during flow. Rheo-optical and dielectric techniques are being used for this purpose, recently neutron scattering as been added as well. Industrial problems are not restricted to equipment design. Wherever possible, the material to be processed should be formulated to ensure optimal processing behaviour. This requires that the rheological properties and the resulting microstructure can be predicted from the composition of the material and the characteristics of its components. To achieve this goal the relation between composition, microstructure and flow behaviour is studied systematically for the classes of materials mentioned above. POLYMERS: In the area of polymer rheology and processing a wide range of topics is being covered. The emphasis is on materials displaying a complex microstructure during processing. This includes in particular polymeric liquid crystals (LCPs) and immiscible polymer blends. The work on LCPs has resulted in a detailed picture of their rheology, in particular of their transient behaviour for which specific scaling laws could be derived. This could be in part related to structural mechanisms. Similarly scaling laws and structural models have been developed for the transient behaviour in immiscible blends. The effects of droplet deformation, break-up and coalescence could be identified and quantified. As a results rheological procedures became available for the micostructural characterization during flow. Rheo-optical characterization procdures for dilute blends have also been developed to study the effect of material properties onstructural changes during flow. This work is being extended from model systems to industrial belnds and from uncompatibilized to in-situ compatibilization (in collaboration with the Chemistry Department). Among the smaller projects, a collaboration with the Faculty of Medicine for the use of bone cement in total hip arthroplasty should be mentioned. SUSPENSIONS: In the suspension area the research has been focused on understanding and predicting the flow behaviour of colloidal suspensions. The rheology of sterically stabilized colloids has been mapped out systematically, using well designed model systems. The role of the stabilizer layer has been described quantitatively and characterization procedures have been presented. Rheo-optical techniques have been used to proof the role of hydrodynamic aggregates in shear thickening and to establish the presence of a particular, unknown 'bundle' phase.
