Berlin 2024 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 34: Emerging Topics in Chemical and Polymer Physics, New Instruments and Methods I

CPP 34.12: Vortrag

Donnerstag, 21. März 2024, 12:45–13:00, H 0106

Near-surface free volume in polymers characterized by positron annihilation lifetime spectroscopy — •Christoph Hugenschmidt¹, Maik Butterling², Vassily Vadimovitch Burwitz¹, Adrian Langrehr¹, Lucian Mathes¹, Eric Hirschmann², Oskar Liedke², and Andreas Wagner² — ¹Heinz Maier-Leibnitz Zentrum (MLZ), Technical University of Munich, Lichtenbergstr. 1, 85748 Garching, Germany — ²Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, 01328 Dresden, Germany

Positron annihilation lifetime spectroscopy (PALS) is a powerful technique for characterizing the free volume in polymers. The main drawback of conventional PALS, however, is the presence of a so-called source component due to positrons annihilating in the radioactive source material. By using a pulsed monoenergetic positron beam, as provided by MePS at the HZDR, the variable positron energy allows the depth-resolved PALS and the spectra intrinsically do not contain a source component. In order to investigate the mean pore size in various polymers, we recorded PALS spectra for positron implantation energies between 0.5 and 10 keV. The measured so-called pick-off lifetime of ortho-positronium allowed us to unambiguously determine the mean void size in the bulk. By analyzing the recorded PALS depth profiles changes of the free volume in the near-surface region of, e.g. polypropylene and polycarbonate could be observed.

Keywords: positron annihilation; free volume; polymers