Regensburg 2007 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 20: Poster session

MM 20.24: Poster

Dienstag, 27. März 2007, 14:45–18:00, Poster C

Nucleation kinetics in deionized charged colloidal model systems: a quantitative study by means of classical nucleation theory — •Patrick Wette¹ and Hans Joachim Schöpe² — ¹Institut für Materialphysik im Weltraum, Deutsches Zentrum für Luft- und Raumfahrt, 51170 Köln — ²Institut für Physik, Johannes Gutenberg Universität , Staudinger Weg 7, 55128 Mainz

We have studied the nucleation kinetics of charged colloidal model systems under salt free conditions covering a wide range of particle number densities 18µm⁻³ ≤ n ≤ 66µm⁻³.We employed direct video-microscopic observation of individual nucleation events to obtain time resolved nucleation rate densities. Polarization microscopy and static light scattering on the resulting solids in combination with Avrami-theory is used to determine the steady state nucleation rate at high undercoolings. The final nucleation rate densities J from different methods are observed to be consistent with each other. By increasing the difference in the chemical potential between melt and crystal Δµ about one order of magnitude J increases over eight orders of magnitude. The data can be well analyzed and interpreted using classical nucleation theory (CNT) leading to a linearly increasing melt/crystal surface tension. Surprisingly the reduced surface tension is about one order of magnitude larger compared to other system (metals, hard sphere colloids). The critical radius of the crystal nuclei is decreasing down to a very small value of 1.5 coordination shells. The determined kinetic prefactors are up to 15 orders of magnitude smaller than the prefactor calculated by CNT.