Berlin 2012 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Colloids and Complex Liquids I

CPP 28.10: Vortrag

Mittwoch, 28. März 2012, 17:45–18:00, C 130

DYNAMICAL SIGNATURE OF CRITICALITY IN COLLOIDAL HARD SPHERE LIKE FLUIDS — Markus Franke and •Hans Joachim Schöpe — Johannes Gutenberg Universität Mainz, Institut für Physik, Staudinger Weg 7, 55099 Mainz, Germany

The particle dynamics of a metastable liquid differs significantly from a liquid in the equilibrium state, giving the possibility to define the freezing point of the system of interest. Dynamic light scattering gives access to the intermediate scattering function (ISF) which measures particle number density fluctuations. Another aspect of the dynamics is the correlation of particle currents dictated by conservation of particle number density, which can be obtained by numerically differentiating the ISF. Recently it was shown that it is possible to define a dynamic freezing criterion in colloidal hard sphere systems by a careful analysis of the space time correlation function of longitudinal particle currents (CCF) [1]. We used highly cross-linked polystyrene (PS) microgel colloids dispersed in a good solvent to obtain a colloidal model system with hard sphere like interaction. We studied the dynamics of the colloidal fluid around the main structure factor peak (1.7<qR<5) over a wide concentration range crossing the freezing transition. Like in a PMMA hard sphere system we observe an universal scaling of the CCF for the equilibrium fluid, while deviations from this scaling were found once the suspension is in the metastable state. Furthermore it is observed that the decorrelation of the CCF becomes nonmonotonic at the structure factor peak if the fluid becomes overcritical. [1] W. van Megen, V. A. Martinez, and G. Bryant, PRL 103, 258302 (2009)