Positron annihilation: a unique method for studying polymers

Positron annihilation is a unique technique for studying the local free volume of polymers. Employing the positron annihilation lifetime spectroscopy (PALS) the size and size distribution of subnanometer size holes which constitute the excess free volume may be studied. In combination with macroscopic volume data the fractional free volume and the number density of holes may be estimated. After presenting the principles of the method, some examples typically for the investigation of the free volume in polymers will be given. Moreover, the study of interdiffusion in demixed polymer blends and further applications are shortly reviewed     

On splitting of dislocations at a reverse motion in germanium single crystals

The dislocation dissociation after the reverse motion along a slip plane in Ge single crystals have been investigated. It has been established that the dissociation width as well as the constriction density were independent on the motion direction. The results obtained have been used to clarify the role of the dislocation splitting in the formation of the phenomenon of the dislocation mobility asymmetry.