Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: SYMPOSIUM Driven Soft Matter I

CPP 16.5: Talk

Tuesday, February 26, 2008, 11:30–11:45, C 130

Rheology and particle tracking on soft colloidal suspensions with tunable glassines — Eko Hari Purnomo, •Dirk van den Ende, Michel Duits, Siva Vanapalli, and Frieder Mugele — Physics of complex fluids, University of Twente, the Netherlands

We studied both the macro- and micro- rheology of soft thermosensitive microgel suspensions that can be tuned continuously and reversibly between the glassy state at low and the liquid state at high temperature. In the glassy state, the rheological properties (G^′ , G^{′ ′} , and J) of the suspensions depend strongly on their age [1]. They can be described quantitatively by the soft glassy rheology (SGR) model. The underlying mechanism for the aging is the increase of the structural relaxation time τ _s as the system ages. To test for micro-rheological propertiesc we determined the mean square displacement (MSD) of probe particles, embedded in the system. The MSD values were obtained from particle tracking using a Confocal Scanning Laser Microscope. This technique provides not only the MSD values but also the displacement distributions and the time evolution of single particle displacements, which are indicative for heterogeneity of the suspension. In this paper we will discuss the non Gaussian properties of our suspension at different levels of glassines as well as the relation between these properties and the macro-rheology.

[1] E.H. Purnomo, D. van den Ende, J. Mellema, and F. Mugele, Phys. Rev. E. 76, 021404 (2007).