LIFETIME DISTRIBUTIONS IN PEO OMMA BLENDS - DEPENDENCE ON AGING TIME/

Positron annihilation lifetime spectroscopy was used to study the time dependence of the ortho-positronium lifetime and intensity and the or tho-positronium lifetime distribution in a poly(ethylene oxide)/poly(m ethyl methacrylate) blend after heat treatment. The recently introduce d maximum entropy for lifetime analysis (MELT) program and the POSITRO NFIT 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. With time, the hole size decreases, while the ortho-positronium intensity remains constant. The lifetime distribution width does not vary systematically with time. Differential scanning calorimetry measu rements show that crystallisation of the poly(ethylene oxide) phase oc curs parallel to the decrease in ortho-positronium lifetime.