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In situ characterization of moisture sorption/desorption in thin polymer films using optical waveguide spectroscopy |
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| Authors: | Li-Qiang Chu Hai-Quan Mao |
| Affiliation: | a Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany b Department of Materials Science and Engineering, National University of Singapore, Singapore 117576, Singapore c Department of Chemistry, National University of Singapore, Singapore 117543, Singapore d Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, MD 21218, USA |
| Abstract: | The kinetics of moisture sorption/desorption in poly(terephthalate-co-phosphate) thin films was investigated in situ at T = 25 °C using optical waveguide spectroscopy (OWS). At low water activities, Fickian diffusion was observed for the initial phase of the sorption process, while at high activities, due to the clustering of water, a complex sorption behavior was found. The moisture sorption isotherms were analyzed according to both the Zimm and Lundberg model as well as the Brown model, which suggests the formation of clusters of water molecules in poly(terephthalate-co-phosphate) at water activities of α1 = 0.58 or higher. The water diffusion coefficient decreases with increasing water activity, which also suggests water cluster formation. A biphasic desorption behavior was also observed upon decreasing the water activity from α1 = 1 to 0. This study demonstrated the unique advantages of OWS in characterizing in situ the sorption/desorption behavior of penetrants in polymer thin films. |
| Keywords: | Moisture sorption/desorption Optical waveguide spectroscopy Poly(terephthalate-co-phosphate) |
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