Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 47: Heterogeneous Nucleation and Microstructure Formation (related to SYMF, jointly with MM)
CPP 47.2: Vortrag
Freitag, 18. März 2011, 10:45–11:00, ZEU 160
Microstructures of a binary mixture of charged colloidal spheres with eutectic phase behaviour — •Thomas Palberg, Nina J. Lorenz, and Izidor Lorencak — Johannes Gutenberg Universität Mainz, Institut f. Physik, Staudingerweg 7, 55128 mainz
Using Microscopy and static light scattering we determined the phase behavior and the occurring microstructures in a binary mixture of charged colloidal spheres with a size ratio of Γ = 0.57. The eutectic point is observed at a molar fraction of small particles xS= 0.8 and total number densities of about (30−40)µ m−3, which is one, resp. two orders of magnitudes larger than the freezing densities of the pure small (S) resp. large (L) particles. In the present system density and composition fluctuations needed for (heterogeneous) nucleation of coexisting S- and L-crystals are coupled to differential sedimentation. Under fluid-solid coexistence conditions we observe the majority component of small particles to form faceted crystals (at xS = 0.9−0.97) in the bulk of the samples, while the minority component of large particles forms a network of rough, bottom wall based, hemispherical cap crystals. No faceting is observable for other mixing ratios and for the pure component systems at coexistence conditions. At number densities well above the eutectic density a correlated solidification scenario is observed, in which both species form a mosaic with intersection facets of columnar crystals growing from the container walls. Similarities and differences to morphologies observed for metallic eutectics are discussed.