Materials characterization of free volume and void properties by two-dimensional positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) has been widely used to determine the free volume and void properties in polymeric materials. Recently, a two dimensional positron annihilation lifetime spectroscopy (2D-PALS) system has been developed for membrane applications. The system measures the coincident signals between the lifetime and the energy which could separate the 2 gamma and 3 gamma annihilations and improve the accuracy in the determination of the free volume and void properties. When 2D-PALS is used in coupling with a variable mono-energy slow positron beam, it could be applied to a variety of material characterization. Results of free volumes and voids properties in a multi-layer polymer membrane characterized using 2D-PALS are presented.