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Positron Annihilation: A New Method for Studying Subnanometer-Size Local Free Volumes in Polymers

: Dlubek, G.; Fretwell, H.M.; Meyendorf, N.


Clyne, T.W. ; Federation of European Materials Societies; Deutsche Gesellschaft für Materialkunde e.V. -DGM-, Oberursel:
Metal matrix composites and metallic foams
Weinheim: Wiley-VCH, 2000 (EUROMAT '99 5)
ISBN: 3-527-30126-7
European Conference on Advanced Materials and Processes and Applications (EUROMAT) <1999, München>
Conference Paper
Fraunhofer IZFP ()
Positronenannihilation; positron annihilation; polymer; polymer; nanostructure; Nanostruktur

Positron/positronium annihilation spectroscopy is a unique tool to probe free-volume holes which apear in amourphous polymers due to the irregular molecular packing. The positron lifetime spectroscopy provides information on the mean hole size and on the hole size distribution which may be studied as a function of temperature, content of plasticizer of humidity, composition of copolymers and blends etc. Typical hole sizes lie in the range r=0.2 - 0.4 nm and v=0.05 - 0.4 nm³. By comparing the coefficients of thermal expansion of specific and of hole volume in PE and PTFE, a fractional free (hole) volume at Tg of ~5% and a hole number of 0.5 - 1 nm³ are estimated. The variation of the hole volume with composition is studied for CR39- and ethylene-vinyl actetate (EVA) copolymers.