Phenomenological treatment of dynamic glass transition heterogeneity

It is an open question whether the slow regions or the fast regions of dynamic glass transition heterogeneity display the continuous part of a cell structure. Recent multidimensional NMR experiments of the Spiess group [U. Tracht et al., Phys. Rev. Lett. 1998, 81, 2727] could determine the characteristic length for poly(vinyl acetate), 3 ± 1 nanometers, but could not decide this question. This paper tries to resolve this question with the aid of a model published in this journal 20 years ago. The phenomenological treatment leads to a Levy distribution for the spectral density of volume fluctuation. The connection between mobility and local density by means of free volume identifies the preponderating component of the Levy distribution with a Glarum defect. This implies that far below the crossover region the continuous part has the lower mobility. Other arguments supporting this picture are collected. The model gives also the size distribution of cooperatively rearranging regions (CRRs) as a function of temperature.