Studies of interdiffusion in polymer blends by PALS

It is shown that positron annihilation parameters such as the average positron lifetime τ av and the ortho-positronium intensity I 3 respond to chemical inhomogeneities in disperse blends and their disappearance due to mutual diffusion of molecules of both phases, when Ps formation is inhibited by one of the constituents. This effect can be used to study mixing in initially demixed compatible blends, demixing in initially mixed incompatible blends, and phase diagrams. With a slow positron beam the concentration-distance profile in thin planar double layer films may be scanned systematically.