On the relationships between guest molecular dynamics and free volume in a series of small molecular and polymer glass-formers

The combined local dynamics and free volume investigations in a series of fourteen glass-formers by means of electron spin resonance (ESR) and positron annihilation lifetime spectroscopy (PALS) are presented. The reorientation of the spin probe TEMPO is related to the annihilation of the ortho-positronium (o-Ps). It was found that the slow to fast transition at T50G is characterized by the almost constant o-Ps lifetime, τ3(T50G) = 2.17 ± 0.15 ns. Then, this transition is connected with the occurrence of the mean free volume hole fluctuation of Vh(T50G) = 114 ± 15 Å3 nearly independent of the chemical and topological character of the matrix constituents as well as of the type and extent of intermolecular interactions.