Journal Article

FZJ-2023-01307

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Determination of Cooperativity Length in a Glass-Forming Polymer

Chua, Y. Z. ; Zorn, R. (Corresponding author)FZJ* ; Schmelzer, J. W. P. ; Schick, C. ; Holderer, O.FZJ* ; Zamponi, M.FZJ*

2023
American Chemical Society Washington, DC

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Please use a persistent id in citations: http://hdl.handle.net/2128/34210  doi:10.1021/acsphyschemau.2c00057

Abstract: To describe the properties of glass-forming liquids, the concepts of a cooperativity length or the size of cooperatively rearranging regions are widely employed. Their knowledge is of outstanding importance for the understanding of both thermodynamic and kinetic properties of the systems under consideration and the mechanisms of crystallization processes. By this reason, methods of experimental determination of this quantity are of outstanding importance. Proceeding in this direction, we determine the so-called cooperativity number and, based on it, the cooperativity length by experimental measurements utilizing AC calorimetry and quasi-elastic neutron scattering (QENS) at comparable times. The results obtained are different in dependence on whether temperature fluctuations in the considered nanoscale subsystems are either accounted for or neglected in the theoretical treatment. It is still an open question, which of these mutually exclusive approaches is the correct one. As shown in the present paper on the example of poly(ethyl methacrylate) (PEMA), the cooperative length of about 1 nm at 400 K and a characteristic time of ca. 2 μs determined from QENS coincide most consistently with the cooperativity length determined from AC calorimetry measurements if the effect of temperature fluctuations is incorporated in the description. This conclusion indicates that─accounting for temperature fluctuations─the characteristic length can be derived by thermodynamic considerations from the specific parameters of the liquid at the glass transition and that temperature does fluctuate in small subsystems.

Keyword(s): Basic research (1st) ; Soft Condensed Matter (2nd)

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Contributing Institute(s):

1. Neutronenstreuung (JCNS-1)
2. Neutronenstreuung und biologische Materie (IBI-8)
3. JCNS-4 (JCNS-4)
4. JCNS-FRM-II (JCNS-FRM-II)
5. Heinz Maier-Leibnitz Zentrum (MLZ)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ) (POF4-6G4) (POF4-6G4)

Experiment(s):

1. J-NSE: Neutron spin-echo spectrometer (NL2ao)
2. SPHERES: Backscattering spectrometer (NL6S)

Appears in the scientific report 2023

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Database coverage:
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