Evaluation of nonuniformity of polymeric membrane materials by positron annihilation technique

Positron annihilation lifetime distribution was experimentally studied in s ome polymers, including polymeric membrane materials, in an air and a nitro gen atmosphere. Basic attention was paid to the long-lived distribution com ponent, i.e., to annihilation of orthopositronium (the positron-electron bo und system). It was found that ambient oxygen affects the annihilation char acteristics of positronium. Newly developed ideas on the mechanisms of form ation, localization, and annihilation of positronium in the polymers lead t o the conclusion that the distribution of free volumes of different size in the polymeric matrix is not uniform. The number concentration and size of free-volume holes and the size of microirregularities containing these hole s were determined.