Phenomenological treatment of dynamic glass transition heterogeneity

It is an open question whether the slow regions or the fast regions of dyna mic glass transition heterogeneity display the continuous part of a cell st ructure. Recent multidimensional NMR experiments of the Spiess group [U. Tr acht et al; Phys. Rev. Lett. 1998, 81, 2727] could determine the characteri stic length for poly(vinyl acetate), 3 +/- 1 nanometers, but could not deci de this question. This paper tries to resolve this question with the aid of a model published in this journal 20 years ago. The phenomenological treat ment leads to a Levy distribution for the spectral density of volume fluctu ation. The connection between mobility and local density by means of free v olume identifies the preponderating component of the Levy distribution with a Glarum defect. This implies that far below the crossover region the cont inuous 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. temperature.