Effect of CO2 exposure on free volumes in polystyrene studied by positron annihilation spectroscopy |
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| Authors: | Hongmin Chen Mei‐Ling Cheng Y C Jean L James Lee Jintao Yang |
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| Institution: | 1. Department of Chemistry, University of Missouri‐Kansas City, Kansas City, Missouri 64110;2. Department of Chemical Engineering and Materials Science, Yuan‐Ze University, Chung‐Li 320, Taiwan;3. Center of Membrane Technology, Chung‐Yuan Christian University, Chung‐Li 320, Taiwan;4. Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, Ohio 43210 |
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| Abstract: | Free‐volume properties, size and distribution, in amorphous polystyrene exposed to CO2 gases have been measured as a function of pressure to 800 psi (5.5 MPa), of time, and of temperature using positron annihilation lifetime spectroscopy. The free volume increases significantly and its distribution broadens as a function of pressure. The free volume relaxes as a function of time with a characteristic time of 15 h, and 5.7 h for 400, and 800 psi, respectively, after depressurizing under vacuum. A portion of free volume created by CO2 exposure remains permanently in the polymer after CO2 exposure. The glass transition temperature decreases significantly as a function of CO2 pressure from the free‐volume data and is compared with the differential scanning calorimeter results. The observed free‐volume variations as a function of pressure, time, and temperature are discussed in terms of hole expansion, creation, free‐volume relaxation, plasticization, and hole filling in amorphous polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 388–405, 2008 |
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| Keywords: | absorption free volume glass transition polystyrene positron annihilation |
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