Determination of key parameters of nucleation from optical investigations of mesoscopic models

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This project aims at the determination of the key parameters of nucleation (interfacial tension, kinetic prefactors, melt structure and undercooling) in systems of single component and binary colloidal shear melts. These systems are highly analogous to atomic and in particular metallic systems, but by contrast, display a convenient accessibility via optical techniques like microscopy, light and small angle x-ray scattering. Based on the work of the first funding period, where the phase behaviour, the melt structure and the nucleation kinetics were studied for a number of selected systems, we now want to apply the successfully tested techniques to dispersions showing bcc/fcc phase boundaries, compound formation and/or eutectic features. All these features are common in metals. Our results for interfacial energies should be directly comparable to those obtained in metals (in particular for Fe-rich alloys), but also to models accounting explicitly for the melt structure which we obtain from USAXS measurements. Pre-factors will be investigated in dependence on “undercooling” using an Arrhenius evaluation of measured homogeneous rate densities. This will allow to discuss the possible involvement of collective dynamics in the nucleation process.