Glass transition models based on heterogeneity

In the AG theory, z defines the size of a cooperatively rearranging region (CRR) at Tg, which is necessarily its maximum value. Donth (1982) has evaluated the size of a CRR by assuming that the region is sufficiently big for the application of thermodynamic relations. From fluctuation theory, 

This analysis also yields Rvalues of 1-2 nm. A significant feature to note 

In the following, glass transition models which recognize the presence of heterogeneity in glass structure, are discussed. 

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