Positron annihilation spectroscopy coupled with a variable mono-energetic positron beam has been used to investigate surface and interfacial properties in thin polymeric films and coatings in recent years. Free-volume properties (size, distribution, fraction, and structure) have been measured from ortho-Positronium lifetime and the S parameter of Doppler broadening of energy spectra from annihilation radiation as a function of the depth (from the surface, interfaces, and to the bulk) and of the temperature in nano-scale polymeric films. A significant lower (17 K), and (11 K) of glass transition temperature than the bulk is observed near the surface and interface, respectively, in an 80 nm polystyrene film on Si substrate. This is interpreted as the different degree of free-volume distribution as a function of depth in nano-scale polymeric films. Recent results in the applications of positron annihilation spectroscopy to analyze multi-layer and chemical nanostructures of composite materials and membrane systems using positron spectroscopy will be presented.

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