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The Role of Elasticity in the Anomalous Swelling of Polymer Thin Films in Density Fluctuating Supercritical Fluids

Tadanori Koga,*^† Y.-S. Seo,^† K. Shin,^‡ Y. Zhang,^† M. H. Rafailovich,*^† J. C. Sokolov,^† B. Chu,^†^§ and S. K. Satija^#

Department of Materials Science & Engineering, State University of New York at Stony Brook, Stony Brook, New York 11794-2275; Department of Materials Science and Engineering, K-JIST, Kwang-ju, 500-712 Korea; Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400; and Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899

Macromolecules, 2003, 36 (14), pp 5236–5243

DOI: 10.1021/ma021265w

Publication Date (Web): June 10, 2003

Abstract

In situ neutron reflectivity was used to investigate the effects of density fluctuations on the solubility of supercritical carbon dioxide (scCO₂) in polymer thin films. Deuterated polystyrene, deuterated polybutadiene, and the corresponding random copolymer, deuterated styrene-random-butadiene copolymer, as well as deuterated poly(methyl methacrylate) were investigated. Data were obtained as a function of pressure under two isothermal conditions (T = 36 and 50 °C). All the polymer films used showed anomalous swelling and CO₂ sorption on the density fluctuation ridge in the P−T phase diagram of CO₂. We found that the magnitude of the swelling was a function of the elasticity of the films rather than the bulk solubility of CO₂. The enhanced miscibility of the rubber/CO₂ systems, which are very poor in bulk, was found to be almost identical to that of the silicon rubber/CO₂ mixture, which is one of the highly miscible polymeric materials under moderate CO₂ conditions.