Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: Poster: Colloids and Complex Liquids

CPP 16.29: Poster

Tuesday, March 27, 2012, 18:15–20:45, Poster A

Formation and Observation of geometric defects in 2D colloidal systems. — •David Polster, Georg Maret, and Peter Keim — Department of Physics, University of Konstanz, D-78464 Konstanz, Germany

In two-dimensional systems topological defects always occur as dislocation, pairs of dislocation or disclinations. These defects appear already near kbT and distort the hexagonal symmetric of the 2D crystal, whereby, according to the Kosterlitz-Thouless-Halperin-Nelson-Young theory, melting in 2D proceed. On the other hand so called geometric defects as isolated point defects need a lot more energy to be created which can experimentally be done with an optical tweezer. We study the particle configurations and the displacement fields of several defects in a 2D system of paramagnetic colloidal particles which are sediment to a water/air-interface. By applying a magnetic field perpendicular to the interface the particles form a 2D crystal with hexagonal symmetry which can be manipulated with an optical tweezer. Thereby, we are interested as well in vacancies as in interstitials and their interaction. Furthermore we study the formation of defect strings by creating more than two defects of the same kind, which rearrange and form a string consisting of two dislocations and a number of vacancies or interstitials in between.