Abstract
Multidimensional echo NMR experiments on polymers are reported that yield insight into the nature of the non-exponential relaxation above the glass transition. By comparing a two-time correlation function to a four-time correlation function, the timescale of fluctuations within the heterogeneous contribution of the rate distribution is analyzed for poly(methyl methacrylate). In agreement with recent measurements on various glass-forming materials fluctuations are observed on the same time scale as the relaxation rates themselves. Furthermore a method is presented which allows one to determine whether the relaxation is mainly heterogeneous or homogeneous by comparing a two-time and three-time correlation function. It turns out for poly(styrene) that the reorientational dynamics is mainly heterogeneous.
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Heuer, A., Kuebler, S.C., Tracht, U. et al. Multidimensional NMR experiments to observe the nature of non-exponential relaxation in glasses. Appl. Magn. Reson. 12, 183–191 (1997). https://doi.org/10.1007/BF03162185
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DOI: https://doi.org/10.1007/BF03162185