(172b) Characterization of Mechanical Proerties of Soft Micro- and Nanoparticles by Analytical Centrifugation

Mechanical properties of microcapsules and microparticles are of practical importance for application of encapsulated materials and of general interest for characterisation of materials used in microencapsulation technology. We report on a new method, based on an analytical centrifuge (LUMiFuge), which was employed successfully to study mechanical properties of different microcapsules, nano- and microparticles as well as biological cells. The separation and packing course during the centrifugation is automaticly recorded by space and time resolved extinction profiles. From this data software obtaines demixing velocity and sediment height (sediment packing concentration). Centrifugal accelaration ramps may be programmed. We demonstrate experiments with biological cells, gel like microcapsules, beads with encapsulated cells and nanoparticles. Results obtained by this method allowed to distinguish between rigid and deformable capsules and cells, to quantify the softness of particles and to quantify packing and compression behaviour. Furthermore we found that some objects relax after reducing the centrifugal acceleration (excess pressure) and show a pronounced dilation behaviour.