Dresden 2014 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 13: Poster - Glasses / Stat. Phys. Bio. / Networks (joint session DY/BP/CPP/SOE)
DY 13.11: Poster
Tuesday, April 1, 2014, 09:30–12:30, P1
Compressed exponential decays in correlation experiments: The influence of temperature gradients and convection — •Jan Gabriel, Thomas Blochowicz, and Bernd Stühn — Institut für Festkörperphysik, Darmstadt
In a wide range of correlation experiments using laser light or partially coherent X-rays so called compressed exponential correlation functions were reported [1] i.e. decays c(τ) ∝ exp(−(t/τ)β) with β>1. The source of this phenomenon is still a point of discussion. For example for colloidal particles in supercooled liquid [2] it is claimed that near Tg hyperdiffusive behavior appears, which leads to compressed correlation functions.
We performed multispeckle-dynamic light scattering experiments in a temperature range from 230 K to 300 K with a sCMOS camera in a system of Polystyrene spheres in supercooled propanediol. At low temperatures compressed exponential decays are observed. At the same time, however, the speckle pattern shows indication for convection in the sample due to a slight temperature gradient, across the sample cuvette mounted on a cold finger cryostat. These effects increase with decreasing temperature and after a temperature jump and can be corrected for by assuming convective flow at constant velocity. Such corrections reduce or remove compressed exponential behavior.
[1] A Madsen, R. L. Leheny, H. Guo, M Sprun and Orsolyal, New J. Phys., 12, 055001 (2010)
[2] C. Caronna, Y. Chushkin, A. Madasen and A. Cupane, Phys. Rev. Lett., 100, 055702 (2008)