LAUSR

Abstract Dispersion based formulations have a broad and diverse range of uses, e.g. for construction materials, paints, cosmetics, food and pharmaceuticals. Gravity driven processes potentially may affect their spatial and temporal composition and this way their appearance and functionality. Therefore physical stability has to be evaluated and predicted in process of development and quality control. For products with shelf life of several month or even years accelerated testing using analytical centrifugation is one option. For this purpose dependence of separation velocity on acceleration applied has to be characterized, which is also important for solid-liquid and liquid–liquid separation processes in centrifugal field. However, situation in case of non-Newtonian liquids is complex and not yet completely understood. Another, but related problem is structuring of dispersion based formulations after production and filling processes over time of storage until final use. From an experimental point of view it is very difficult to investigate this process without breaking these soft structures during sampling for measurement. In this paper we describe investigations into both, separation behaviour of particles dispersed in non-Newtonian continuous phase in dependence on gravity and aging of dispersions during storage. To this end we chose suspensions of nearly monosized silica particles in pectin solutions as model system. Separation behaviour of freshly prepared model dispersions was investigated as function of pectin concentration and centrifugal acceleration. To visualize and quantify aging of dispersions they were filled into cells after preparation and stored for aging different times before measuring separation behaviour in centrifugal field. This way the process of structure build up can be investigated quasi in-situ. Results are presented regarding particle separation of suspensions formulated of non-Newtonian continuous phases in dependence on centrifugal acceleration. The model system allows to investigate the separation in non-Newtonian fluids in centrifugal field, determine actual apparent viscosity of pectin solutions and study interaction between biopolymer and particles (flocculation).