Application of Positron Annihilation Lifetime Spectroscopy in Studies of Polymer Composites

A brief review of the concept of the free volume and its fraction in polymer composites is presented. The experimental results obtained using positron lifetime spectroscopy for the detection of these volumes in two composites of poly(glycolide-co-L-lactide) with bioactive glasses and mixes of ethylene propylene diene monomer and surface-modified precipitated silica are discussed in more detail. It is demonstrated that the free volume fraction exhibits a linear relationship with the bioactive glass content in the first composite. However, in general, deviations from linearity can be induced by the presence of the interfacial regions between the filler and the polymer matrix. Additionally, the Psc_12 computer program, which calculates radii of free volume holes, pores, and capillaries from the values of the ortho-positronium pick-off annihilation lifetime, is described in detail.