Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 11: POSTER Disperse Polymer Systems

CPP 11.35: Poster

Tuesday, March 28, 2006, 17:00–19:00, P3

Structure and dynamics of electrostatically interacting magnetic colloidal suspensions by means of static and dynamic x-ray scattering — •Tina Autenrieth¹, Joachim Wagner², Aymeric Robert³, and Gerhard Grübel¹ — ¹Hasylab at DESY, Notkestrasse 85, 22607 Hamburg — ²Universität des Saarlandes, Saarbrücken — ³ESRF, Grenoble, France

A model system for complex liquids with dipolar interactions has been synthesized [1]. The particles consist of a magnetic cobalt ferrite core embedded in a silica shell and have a narrow size distribution. They interact due to the charged silica surface via a screened Coulomb potential in addition to the magnetic dipole-dipole interaction of the core. The colloidal suspension is strongly opaque and thus cannot be probed by visible light scattering techniques. Therefore both, the static and dynamic behaviour of such a concentrated, liquid-like ordered dipolar suspension are studied by means of Small Angle X-ray Scattering and X-ray Photon Correlation Spectroscopy without and in the presence of an external magnetic field [2]. The dynamics was probed over the Q-range of the static structure factor and shows even without magnetic field strong deviations from the Stokes-Einstein behaviour that can not be explained by the De-Gennes narrowing. The observed behaviour has to be attributed to indirect hydrodynamic interactions which are mediated by the suspending medium [3]. However, the hydrodynamic behaviour cannot be described by any of the available models for colloidal hydrodynamics. [1] T. Autenrieth et al., AOC 18, 520 (2004) [2] J. Wagner et al., JMMM 289, 54 (2005) [3] A. Robert et al., JCP 122, 084761 (2005)