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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 26: INTERNAL SYMPOSIUM Optical Spectroscopy I
CPP 26.6: Vortrag
Donnerstag, 29. März 2007, 12:00–12:15, H40
Large-scale heterogeneity in supercooled glycerol probed by single-molecule fluorescence and by rheology — •Florian Kulzer1, Rob Zondervan1, Ted Xia1, Harmen van der Meer1, Cornelis Storm2, Wim van Saarloos2, and Michel Orrit1 — 1Leiden Institute of Physics, Leiden University, P. O. Box 9504, NL – 2300 RA Leiden — 2Instituut – Lorentz for Theoretical Physics, Leiden University, P. O. Box 9506, NL – 2300 RA Leiden
We employ variable-temperature single-molecule microscopy to study heterogeneity in supercooled glycerol in the temperatures range of 5 to 25 K above the glass transition (Tg=190 K). By following the rotational diffusion of perylene guest molecules we get direct access to the distribution of local viscosities, which vary by a factor of five or more for different individual fluorophores at a given temperature. By following the same single molecules at various temperatures, we find that the distribution of local viscosities itself broadens upon approaching the glass transition temperature. This spatial heterogeneity relaxes extremely slowly and can persist over hours or even days. These results convey a picture of heterogeneous liquid pockets separated by solid-like walls, which exist already well above the viscosimetric glass transition. To corroborate this surprising result, we have conducted rheological measurements to find evidence for the solid-like network in the macroscopic mechanical response of supercooled glycerol. In agreement with the conclusions from our single-molecule experiments, we can detect typical features of soft glassy rheology in the properties of glycerol in the same temperature range.