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Authors
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Xu, B. ; Leisen, J. ; Böhme, U. ; Scheler, U. ; Beckham, H. W.
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Title
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1H NMR T1 Relaxation of polymer/montmorillonite nanocomposites with different clay contents and degrees of exfoliation: magnetic field effects
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Date
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29.10.2012
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Number
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34802
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Abstract
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The initial stage of the NMR H-1 T-1 relaxation of well-defined polypropylene-montmorillonite nanocomposites was investigated at two different magnetic fields of 0.54 and 7.05 T. At 0.54 T, two periods can be distinguished during the first 30 ms after a saturation pulse train. Both periods scale linearly with the square root of the recovery time. The first period occurs during the first 1 ms and is attributed to direct dipolar relaxation of nuclei in immediate proximity to the clay. It is caused by paramagnetic impurities within the clay and is characterized by a magnetization recovery curve with a slope proportional to the concentration of these impurities. The second period occurs at 4 to 30 ms after saturation and is due to spin diffusion between the sink, formed by the initial relaxation at the clay surface, and the surrounding polymer matrix, which relaxes at a much slower rate. The second period is characterized by a magnetization recovery curve with a slope proportional to the effective surface area of the clay, from which a degree of exfoliation may be determined. At 7.05 T, only a single relaxation recovery period is observed. At this higher magnetic field, the direct relaxation is characterized by a substantially longer relaxation time so that it is not distinguished from the spin-diffusion process. As with the slope of the second period of the magnetization recovery at 0.54 T, the slope of the magnetization recovery curve at 7.05 T can be utilized to extract a degree of exfoliation.
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Publisher
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Zeitschrift für Physikalische Chemie
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Wikidata
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Citation
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Zeitschrift für Physikalische Chemie 226 (2012) 1229-1241
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DOI
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https://doi.org/10.1524/zpch.2012.0282
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