Regensburg 2004 – wissenschaftliches Programm

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.97: Poster

Donnerstag, 11. März 2004, 16:00–18:00, Poster D

2-D Crystals on Curved Surfaces — •Peter Lipowsky, Hans-Georg von Ribbeck, Michael G. Nikolaides, and Andreas R. Bausch — TU Muenchen, Physik-Department E22, James-Franck-Strasse, D-85747 Garching

Determining the minimum-energy configuration of repulsive particles on spherical surfaces is a rather difficult problem. Euler’s theorem states that twelve pentagons are required to close a hexagonal network. Theory and computer simulation have shown that, with rising system size, the strain induced by single pentagonal disclinations will be lowered by the introduction of additional pairs of bound 5-7 defects. An experimental system to test the theoretical predictions has been developed. We use surface-modified microspheres self-assembled onto the surface of water droplets in an organic solvent. Crystalline structures are observed as soon as the area density of particles at the interface is high enough. As predicted by theory, we find that these crystals form distinctive high-angle grain boundaries. The number of excess defects in these scars grows linearly with the system size. Using digital video microscopy, particle tracking algorithms, and triangulation routines, the dynamical behaviour of the defects and the movements of single particles in the spherical lattice are explored. The elastic potential of the lattice, the Young modulus, and the diffusion constant are determined. First results demonstrating typical phase transitions between fluid and crystalline phases are presented. Binary mixtures formed by beads of two different diameters at the interface were investigated.