Positron-annihilation lifetime spectroscopy with in-situ control of temperature, pressure and atmosphere to determine the free-volume of soft materials
Ricardo Helm, J. Lehtonen, Michael Mayerhofer, Johannes Mitteneder, Werner Egger, Rhea Verbeke, P. Sperr, G. Dollinger, Marcel Dickmann
Abstract
We introduce a newly developed instrument for 22Na-based positron-annihilation lifetime spectroscopy (PALS) with in-situ temperature, pressure and atmosphere control. The system is designed for PALS measurements of samples in changing atmospheric conditions, from vacuum (∼10−5 mbar) up to a gas pressure of 20 MPa. Furthermore, we can select the composition of the applied gas, such as N2, Ar, Ar/H2, CO2 as well as CH4 and adjust the sample temperature from room temperature to 200 °C. To test the measurement principle, we carried out PALS measurements on semi-crystalline polystyrene in (99.999 %) pure argon atmosphere varying the pressure and the temperature simultaneously, up to 4 MPa and T = 150 °C. Changing the sample environment in that way affects the free-volume of the polymer, which is reflected in the positron lifetime and intensity.