Positron Annilation Lifetime and Glass Transition Temperatures in CO2 Sorption Polystyrene

Y.C. Jean a, b, H. Chen a, L.J. Lee c and J. Yang c a Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110, USA b Center of Membrane Technology, Chung-Yuan Christian University, Chung-Li, Taiwan c Department of Chemical and Biomolecular Engineering, Ohio State University, Columbus, OH 43210, USA

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Received: 3 09 2007;

Positron annihilation lifetime spectroscopy was used to measure the free-volume size and distributions as a function of temperature in polystyrene with and without 400 psi CO2 sorption. The transition temperatures in the polystyrene with CO2 sorption obtained from ortho-positronium lifetimes were found to depend on the thermal cycles and a meta-stable state showing a negative thermal expansion coefficient was observed between 53°C and 82°C during the first heating up experiment. The observed Tg in polystyrene with, and without CO2 sorption after annealing from ortho-positronium lifetimes were found to be 86°C and 91°C, which are 5°C higher, and 10°C lower than from the differential scanning calorimetry data, respectively. The observed free-volume variations are discussed in terms of hole expansion, creation, free-volume relaxation, plasticization, and hole filling in amorphous polymers.

DOI: 10.12693/APhysPolA.113.1385 PACS numbers: 78.70.Bj, 78.66.Qn, 71.60.+z