The analytical centrifuge LUMiSizer as a useful tool for the characterization of nanoparticles

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The analytical centrifuge LUMiSizer allows to speed-up the separation of dispersions by application of a centrifugal force and by raising the temperature (acceleration of diffusion limited processes, decreasing the viscosity). The LUMiSizer employs the STEP-Technology (Space and Time resolved Extinction Profiles), which allows measuring the intensity of the transmitted light as function of time and position over the entire sample height (in the cell) simultaneously. The data (so called transmission profiles) are displayed as a function of the transmittances in the time and the radial position (e.g. the distance from the center of the rotation). The transmission profiles contain the information on stability and on the kinetics of the separation processes and facilitate particle characterization. By means of available analysis modes, the separation and the particle size can be quantify and analysed in detail. At the same time up to 12 different samples can be analysed simultaneously at constant or variable centrifugal force up to 4000 rpm. LUMiSizer allows easily detect/distinguish the aggregated/flocculated/dispersed particles in the dispersion medium. It is one of the candidates to fast and sensitively characterize the affinity of the particle to the liquids. This technique may also be used to determine the (nano)particle hydrodynamic density, particle size distribution etc. The separation process of our nanoparticle dispersion is characterized by the very polydisperse sedimentation (no sharp front) of particles with relatively narrow particle size distribution of fine particles which move with different speed. Polydisperse sedimentation is characteristic for colloidal stable dispersions (stable against particle aggregation). Prior to separation, particle concentration is equally distributed along the complete sample length, i.e. transmission is constant at a low level (first transmission profile with the lowest transmission). As sedimentation proceeds the concentration of particles decreases in the region of meniscus and transmission increases. The last profile (highest transmission) indicates that the smallest particles have not yet fully separated out from the supernatant within the applied centrifugation time. Only the very small sediment is observed due to a dense packing of particles characteristic for colloidal stable systems with the repulsive particle-particle interaction.

LUMiSizer, nanoparticles, sedimentation

DOSKOČIL, L.; SZEWIECZKOVÁ, J.; ENEV, V.; PEKAŘ, M.

21. 10. 2014

978-80-210-7159-9

Frontiers in material and life sciences

113

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