Compressed exponential decays in correlation experiments: The influence of temperature gradients and convection

The Journal of Chemical Physics
Jan GabrielBernd Stühn

Abstract

In a wide range of soft materials, correlation experiments using laser light or partially coherent X-rays report the so called compressed exponential correlation functions, i. e., decays c(t) ∝ exp(-(t/τ)(β)) with β > 1. In many cases, this is related to the relaxation of inner stresses, but in some systems, the source of such a phenomenon is still poorly understood. We performed multi speckle-dynamic light scattering experiments in a system of polystyrene spheres in supercooled propanediol. At low temperatures, compressed exponential decays are observed in a multispeckle experiment, in agreement with the literature findings in similar systems. At the same time, due to the particular geometry of our setup, the speckle pattern shows indication for convection in the sample due to a slight temperature gradient across the sample cuvette mounted in a cold finger cryostat. These effects increase with decreasing temperature and after a temperature jump. In some cases it can be corrected for by assuming convective flow at constant velocity. Such corrections reduce or remove compressed exponential behavior in our experiment.

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Citations

Jun 28, 2017·Proceedings of the National Academy of Sciences of the United States of America·Fivos PerakisAnders Nilsson
Dec 6, 2018·Physical Review Letters·Valentino BiancoPaolo Malgaretti
Oct 4, 2015·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Martin QuickNikolaus Paul Ernsting
May 15, 2020·Physical Chemistry Chemical Physics : PCCP·Jan Philipp GabrielThomas Blochowicz
Mar 3, 2021·Journal of Synchrotron Radiation·Laurence B LurioEric M Dufresne
Nov 23, 2019·The Journal of Physical Chemistry. B·Till BöhmerThomas Blochowicz

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