Analytical Ultracentrifuge

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Analytical Ultracentrifugation (AUC) is a method of colloid analytics, which enables a complete characterization of dispersed systems. Nanoparticles or macromolecules, dispersed in a solvent, are separated in a centrifugal field, while absorption or interference optics allow observing this process in the sample cell. The data evaluation yields the sedimentation and diffusion coefficients, and their distributions, from the sedimenting boundary velocity and broadening, respectively. From these parameters and measurements, particle size, shape as well as molecular weight and sample density are accessible. Interacting systems can also be analyzed by means of AUC; sedimentation-diffusion-equilibrium experiments yield the stoichiometry and equilibrium constant of chemical equilibria.AUC is an absolute method. Due to the fractionation and optical detection of the entire system, data with high statistical significance are obtained. Indeed, AUC is a high-resolution technique, which can resolve differences between particle sizes in the Ångström range. Using modern Rayleigh interference optics, both very dilute and concentrated dispersions can be analyzed. Light absorbing samples can be characterized using multiwavelength absorbance (MWA) detectors, which allows identifying distinct components in complex mixtures. In case of metal and semiconductor nanoparticles, the MWA detector allows characterizing size dependent optical properties (due to plasmon resonance and quantum size effects, respectively) in detail.In this project, the Analytical Ultracentrifuge will be used to address various questions. On one hand, it will serve to study the early stages of the formation of solids from solution, i.e., to characterize smallest clusters, nuclei and intermediates, as well as their interactions with additives, ranging from simple molecules to proteins. On the other hand, the device will be used to answer various questions in the areas of semiconductor nanostructures, multifunctional amphiphiles, porous organic-inorganic solids, complex nanoparticles and nanoparticle superstructures, as well as synthetic polymers, tailor-made for the use in biomaterials. The requested device is literally indispensable for the analyses of the early stages of the formation of solids, and will crucially contribute to answering various questions in the above mentioned fields of chemical materials science.