Regensburg 2016 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 33: Colloids and Complex Fluids IV (Joint Session DY/BP/CPP)
BP 33.4: Vortrag
Dienstag, 8. März 2016, 14:45–15:00, H46
Equilibrium interfacial free energies and Turnbull coefficient for bcc crystallizing colloidal charged sphere suspensions — •Thomas Palberg1, Patrick Wette2,3, and Dieter M. Herlach2 — 1Institut f. Physik, Johannes Gutenberg Universität, 55099 Mainz, Germany — 2Institut f. Materialphysik im Weltraum, DLR, 51147 Köln, Germany — 3Space Administration, DLR, 53227 Bonn, Germany
The interfacial free energy (IFE) is a central quantity in crystallization from the meta-stable melt. In suspensions of charged colloidal spheres, nucleation and growth kinetics can be accurately measured from optical experiments. We here re-analyze the strictly linear increase of previously reported CNT-effective non-equilibrium IFEs estimated from such experimentsutilizing classical nucleation theory (CNT). For five aqueous suspensions of charged spheres and one binary mixture, we utilize a simple extrapolation scheme and interpret our findings in view of Turnbull’s empirical rule. Our first estimates for the reduced equilibrium IFE, σ0,bcc, between coexisting fluid and bcc-crystal phases are on the order of a few kB T. Their values are not correlated to any of the electrostatic interaction parameters but rather show a systematic decrease with increasing size polydispersity and a lower value for the mixture as compared to the pure components. At the same time, σ0 shows an approximately linear correlation to the entropy of freezing. The equilibrium interfacial free energy of strictly monodisperse charged spheres may therefore be still greater.