Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 7: Liquids

CPP 7.1: Vortrag

Montag, 23. März 2009, 18:00–18:15, ZEU 160

Doppler-broadening (DB) measurement of ionic liquids using a monoenergetic positron beam. — •Philip Pikart¹, Christoph Hugenschmidt², and Klaus Schreckenbach² — ¹Physik-Department E21, Technische Universität München, James-Franck-Strasse, 85748 Garching, Germany — ²ZWE FRM II, Technische Universität München, Lichtenbergstrasse 1, 85747 Garching, Germany

In this project, room-temperature ionic liquids are studied by positron annihilation spectroscopy which is a standard method for defect characterization of solid state samples. These "organic salts" contain essentially only weakly coordinated ions, resulting in a remarkably low melting point. One of their key properties is the low vapour pressure of less than 10⁻⁶ mbar at liquid state, wich enables measurements of the bare substances in high-vacuum and therewith the application of positron beam studies. 1-Butyl-3-methyl-imidazolium-hexafluorphosphat is choosen for this study, that has well known thermal properties like glasstransition- and triple-point temperature.

The (C)DB-spectrometer and the high intense monoenergetic positron beam of the NEPOMUC beam facility located at the FRM II in Garching are used. The measurements demonstrate the diffusion effects of positrons in a liquid as well as phase transitions, induced by variation of sample temperature between 80K and 300K during the measurement.