Web Release Date: November 29,
Free Volume in C60 Modified PPO Polymer Membranes by Positron Annihilation Lifetime Spectroscopy
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Lehrstuhl für Materialverbunde, Technische Fakultät der Christian-Albrechts-Universität zu Kiel, Kaiserstrasse 2, 24143 Kiel, Germany, and Faculty of Science and Technology, Membrane Technology Group, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands
Received: June 26, 2007
In Final Form: October 12, 2007
Abstract:
PPO (poly(2,6-dimethyl-1,4-phenylene oxide)) is a well-known membrane material showing good gas separation properties. The incorporation of nanoparticles can enhance or deteriorate the performance of composite membranes, sometimes depending only on the way of the composite preparation. We have modified the PPO polymer with C60 fullerenes up to a content of 2 wt %. Previous investigations showed a strong dependence of permeability on whether the C60 is simply dispersed in the polymer or chemically bonded to the polymer chains. Free volume effects were suggested as an explanation but not experimentally confirmed. Here, we present free volume studies by positron annihilation lifetime spectroscopy. An additional long positron lifetime shows the increased free volume of composite samples, while the high electron affinity of C60 helps to indicate the homogeneity of the samples. Combining the presented results with permeability measurements refines the understanding of this promising membrane material.
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