| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 97 === In this study, dense homogeneous polycarbonate (PC) membranes were prepared via a dry-phase inversion method at different heat treatments and were tested for pure gas permeability of carbon dioxide (CO2). The effect of different gas pressure conditions as well as different heat treatments on the morphologies of dense PC membranes and on their gas permeability performances was studied with the use of positron annihilation spectroscopy (PAS).
There was no noticeable effect on the surface morphologies, chemical structures, glass transition temperatures (Tg), and mechanical properties of the different heat-treated PC membranes, as shown by the SEM, FTIR, DSC, and UMTM data, respectively. However, these heat-treated PC membranes had different gas permeability performances, so we could not characterize the change in their structure at the molecular scale by conventional instruments. The PAS was utilized to detect the free-volume size and the intensity of the heat-treated PC membranes at different gas pressure conditions. The free-volume in the PC membranes has monomodal distribution at atmospheric pressure environment, whereas bimodal free-volume distributions were attained at carbon dioxide pressure environment. The plasticization of carbon dioxide may lead to this phenomenon because there was almost no change in the free-volume size of the PC membranes with increasing pressure at inert gas (helium, He) pressure environment. Based on the analysis of the PAS data in regard to gas permeability performances, it seemed that big pores predominantly controlled the carbon dioxide permeation behavior.
The results showed that the free-volume and the gas permeability of the PC membranes increased with increasing amounts of residual solvent at high carbon dioxide pressure. For the PC membranes with low residual solvent contents above Tg, the gas permeability performance could be affected significantly by antiplasticization, and the free-volume and the gas permeability of the PC membranes decreased with increasing carbon dioxide pressure because the compression effect was predominant.
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