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Kinetic data for structural relaxation in silver iodomolybdates at the glass transition temperature (Tg) are obtained by high-pressure differential scanning calorimetry (HP-DSC) and are compared with activation energies (EA) and volumes (VA) obtained earlier from conductivities below Tg. The results are fitted to an empirical equation, EA = MVA, and displayed in the form of a master plot of EA versus VA, an approach previously applied to strongly coupled systems, including polymer electrolytes and molten salts above their glass transition temperatures. The parameter M emerges as a localized modulus, expressive of interatomic forces within the medium, linking together EA,sigma, VA,sigma and EA,s, VA,s, the "apparent" activation parameters for ionic conductivity and structural relaxation, respectively. The VA and EA values for ion transport are much smaller than the corresponding values for structural relaxation. However, remarkably close agreement emerges between the "process parameters", Ms and Msigma, both close to 8 GPa, thus establishing a quantitative link between ion transport and structural relaxation in this highly decoupled system. A new EA versus VA master plot is constructed, which points the way to a unified approach to ion transport in polymers and glasses.

ABSTRACT:The copolyester poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate) (PETG) is used industrially as an uncrystallizable polymer, whereas PET is an inherently crystallizable polymer. Nevertheless, a crystalline phase could appear in the material. To create a strain-induced crystalline phase in an initially amorphous PETG material, plates were placed in the heating chamber of a tensile machine at 100°C and uniaxially drawn to obtain different samples with various draw ratios. During DSC analysis of highly drawn samples, perturbations of the baseline appear above the glass-transition temperature, consisting of weak exothermic and endothermic phenomena. Comparison of DSC and X-ray diffraction analysis of drawn PETG and PET shows that a strain-induced crystalline phase appears in this copolyester. A spherulitic superstructure could also appear after lengthy annealing. Analysis of this semicrystalline material allowed estimation of the degree of crystallinity, about 3% after a drawing at high draw ratio and about 11% for undrawn annealed material.