Extending the Anomalous Dilation in CO2 to Thick Polymer Blend Films: A Neutron Reflectivity Study

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• 作者：Jaseung Koo ; Tadanori Koga ; Bingquan Li ; Sushil K. Satija ; Miriam H. Rafailovich
• 刊名：Macromolecules
• 出版年：2016
• 出版时间：May 10, 2016
• 年：2016
• 卷：49
• 期：9
• 页码：3433-3441
• 全文大小：546K
• 年卷期：0
• ISSN：1520-5835

文摘

We investigated the effect of density fluctuation of supercritical carbon dioxide (scCO₂) on anomalous swelling of multilayer polymer thin films on the ridge in the pressure–temperature phase diagram of CO₂. In order to measure the swelling ratio along the film depth, we alternately deposited hydrogenated poly(methyl methacrylate) (PMMA) and deuterated polystyrene (dPS) thin films and performed the neutron reflectivity measurements as a function of CO₂ pressure at 36 °C. The results showed that, in contrast to previous studies, CO₂ was to penetrate deeply throughout the multilayer thin film where the magnitude of swelling along the density fluctuation ridge of CO₂ was independent of film thickness. Block copolymer thin films of dPS-b-PMMA with a parallel lamellar orientation also showed similar swelling behavior in scCO₂. However, it is well-known that single-layer polymer thin films exhibit anomalous swelling behavior only near the film surface. This difference is probably due to the fact that the multilayer thin films have the CO₂-philic PMMA layer sandwiched between dPS layers, which can function as a CO₂ reservoir, thereby transferring the CO₂ molecules from the PMMA layers to the adjacent dPS layers. Furthermore, we found that the interaction between polymers and substrates was not significant in scCO₂ from diffusion dynamics results using neutron reflectivity, thereby facilitating anomalous dilation of polymers near the substrates without a pinning effect.