LIFETIME DISTRIBUTIONS IN PEO/PMMA BLENDS : DEPENDENCE ON AGEING TIME

Positron annihilation lifetime spectroscopy was used to study the time dependence of the ortho-positronium lifetime and intensity and the ortho-positronium lifetime distribution in a poly(ethylene oxide)/poly(methyl methacrylate) blend after heat treatment. The recently introduced maximum entropy for lifetime analysis (MELT) program and the POSITRONFIT program were used for evaluation of the spectra. The blend shows a large excess in free volume hole size shortly after cooling from the melt. Withi time, the hole size decreases, while the orthio-positronium intensity remains constant. The lifetime distribution width does njot vary systematically with time. Differential scanning calorimetry measurements show that crystallisation of the poly(ethylene oxide) phase occurs parallel to the decrease in ortho-positronium lifetime.