Characteristic length of glass transition: experimental evidence

Abstract

The glass transition length scale determined from formulae of a fluctuation approach (2ξ_a = 2 ... 5 nm) is confirmed by two independent experimental methods. Firstly the glass transition parameters in self-organized amorphous layers of variable thickness in semicrystalline poly(ethylene terephtalate) show significant sensitivity to the nanometer length scale of ξ_a. The results can be explained by a direct influence of spatial limitations on the large mode lengths of the glass transition. Secondly, the analysis of the arrangement of different system responses across the glass transition zone at constant temperature in polystyrene and poly(vinyl acetate) results in the location of ξ_a between the limits 0.6 nm (from local modes) and 10 nm (entanglement spacing). Experimental temperature dependencies of spectral widths are discussed with those obtained from the fluctuation approach. The report also contains a discussion of the presumed general scaling principle: At a given state, short mode length corresponds to high frequency (mobility) and vice versa.