Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 7: POSTERS Rheology
CPP 7.20: Poster
Monday, February 25, 2008, 16:45–19:00, Poster A
Competition of Phase Separation and Kinetic Arrest in a Binary Mixture with Depletion Attraction — •Anna Kozina1, Pedro Diaz-Leyva1,2, Christian Friedrich1,3, and Eckhard Bartsch1,2 — 1Institute of Macromolecular Chemistry, Freiburg University, Germany — 2Department of Physical Chemistry, Freiburg University, Germany — 3Material Research Centre Freiburg, Freiburg University, Germany
Recently it has been shown that the introduction of short-range attractions by the addition of free polymer leads to such effects like melting of a colloidal glass and appearance of a reentrant glass transition [1] ('attractive' glass). The studied colloidal system consists of a binary colloidal mixture of 1:50 cross-linked polystyrene microgel particles in a good solvent. To introduce short-range attraction various amounts of linear polystyrene were added. A binary mixture was chosen to suppress crystallization and the size ratio Rg,polymer/Rcolloid ~ 0.08 should exclude a fluid-fluid phase separation. Nevertheless, when driving the system into the attractive glass, a pronounced waiting time dependence of both density fluctuations and mechanical properties was observed. Using time resolved SLS we found evidence that this behavior is due to a micro phase separation of A and B particles with the concomitant formation of pure crystalline A and crystalline B micro domains. This phenomenon is reminiscent of the fractionation of polydisperse emulsion droplets via depletion attraction [2].
[1] T. Eckert and E. Bartsch, Phys. Rev. Lett. 89, 125701 (2002) [2] J. Bibette, J. Colloid Interf. Sci. 147, 474 (1991)