Regensburg 2016 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 21: Complex Fluids and Colloids IV (joint session DY/BP/CPP)

DY 21.4: 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 Wette^2,3, 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, σ_0,bcc, between coexisting fluid and bcc-crystal phases are on the order of a few k_B 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.