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Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy

Schramm, S. and Blochowicz, T. and Gouirand, E. and Wipf, R. and Stühn, B. and Chushkin, Y. (2010):
Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy.
In: Journal of chemical physics, pp. 224505-1-224505-10, 132, (224505), [Online-Edition: http://jcp.aip.org/jcpsa6/v132/i22/p224505_s1],
[Article]

Abstract

We investigate structure and dynamics of concentration fluctuations in the binary glass former methyl-tetrahydrofuran and oligomeric methyl metacrylate by photon correlation spectroscopy with partially coherent x-rays from a synchrotron source. Although the system is macroscopically well miscible and optically clear in the full temperature range, calorimetric and dielectric measurements reveal two distinct glass transition temperatures. The relaxation of long range concentration fluctuations turns out to be diffusive and exponential only well above the upper glass transition temperature. As the characteristic time τcf for concentration fluctuations shows a much weaker temperature dependence than the α-relaxation both traces finally intersect upon lowering the temperature. Thus, close to Tg, the concentration fluctuations show pronounced features of out-of-equilibrium dynamics such as compressed relaxation functions and a crossover to a ballistic wave vector dependence of τcf, like previously observed in various soft matter systems. Moreover, the analysis of time-resolved correlation functions reveals that the relaxation of concentration fluctuations around Tg involves pronounced dynamic heterogeneities.

Item Type: Article
Erschienen: 2010
Creators: Schramm, S. and Blochowicz, T. and Gouirand, E. and Wipf, R. and Stühn, B. and Chushkin, Y.
Title: Concentration fluctuations in a binary glass former investigated by x-ray photon correlation spectroscopy
Language: English
Abstract:

We investigate structure and dynamics of concentration fluctuations in the binary glass former methyl-tetrahydrofuran and oligomeric methyl metacrylate by photon correlation spectroscopy with partially coherent x-rays from a synchrotron source. Although the system is macroscopically well miscible and optically clear in the full temperature range, calorimetric and dielectric measurements reveal two distinct glass transition temperatures. The relaxation of long range concentration fluctuations turns out to be diffusive and exponential only well above the upper glass transition temperature. As the characteristic time τcf for concentration fluctuations shows a much weaker temperature dependence than the α-relaxation both traces finally intersect upon lowering the temperature. Thus, close to Tg, the concentration fluctuations show pronounced features of out-of-equilibrium dynamics such as compressed relaxation functions and a crossover to a ballistic wave vector dependence of τcf, like previously observed in various soft matter systems. Moreover, the analysis of time-resolved correlation functions reveals that the relaxation of concentration fluctuations around Tg involves pronounced dynamic heterogeneities.

Journal or Publication Title: Journal of chemical physics
Volume: 132
Number: 224505
Divisions: 05 Department of Physics > Institute for condensed matter physics
05 Department of Physics
Date Deposited: 23 Jun 2010 15:42
Official URL: http://jcp.aip.org/jcpsa6/v132/i22/p224505_s1
Identification Number: doi:10.1063/1.3431537
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