Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 23: Poster session

MM 23.52: Poster

Dienstag, 26. Februar 2008, 14:45–18:00, Poster B

Elasticity and solidification kinetics in a eutectic-like two component colloidal system — •Nina J. Lorenz and Thomas Palberg — Institute of Physics, University of Mainz, Germany

Colloidal systems of charged spherical particles in deionized aqueous suspension show a first order phase transition to a crystalline state (bcc or fcc) once the strength and range of the screened Coulomb repulsion are sufficiently large. Recently we also investigated the phase behaviour of binary charged mixtures using static light scattering, to find random composition bcc crystals at charge and size ratios close to one, the onset of compound formation at ratios below 0.7 and a eutectic-like phase behaviour at ratios around 0.55 with strong indications of a gravitation assisted demixing [1]. The kinetics of the latter mixture was monitored via the evolution of the shear elasticity employing torsional resonance spectroscopy. While the pure components and the mixtures far from the eutectic composition solidify via homogeneous nucleation within a few minutes, closer to the eutectic composition the shear modulus takes days to reach its final value in the completely solidified state. We discuss the coupling of crystallization kinetics to the kinetics of demixing, which depend on both the composition and the 'undercooling' which for our systems is approximately linear in particle concentration.

[1] N.Lorenz, J.Liu, T. Palberg: Phase behaviour of binary mixtures of colloidal charged spheres, Colloids Surf. A (in press 2007)