Transport properties of water in hydroxypropyl methylcellulose |
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Authors: | Charlotte Trotzig Frans HJ Maurer |
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Institution: | a Department of Polymer & Materials Chemistry, Lund Institute of Technology, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden b AstraZeneca R&D, SE-431 83 Mölndal, Sweden |
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Abstract: | The relation between the self-diffusion coefficient, Dself, of water and the free volume hole size, Vh, has been investigated in a hydroxypropyl methylcellulose (HPMC)-water system in the water content range 0.08-0.36 w/w, at room temperature. Furthermore, the thermal properties of the water in the HPMC-water system, as measured with differential scanning calorimetry (DSC) and the tensile storage, E′, and tensile loss, E″, moduli, of the HPMC-water systems, as determined with dynamic mechanical analysis (DMA), have been probed. Pulsed-field gradient nuclear magnetic resonance (PFG NMR) was used to measure the Dself of water and positron annihilation lifetime spectroscopy (PALS) was used to measure the ortho-Positronium (o-Ps) lifetime in the HPMC-water system. The glass transition temperature of the HPMC was found to be reduced by the water to room temperature in the water content range 0.10-0.15 w/w. The relation between ln Dself of water and the inverse free volume hole size of the HPMC-water system was non-linear. Furthermore, the PALS measurements showed that molecular water co-existed with water clusters in the HPMC-water system. |
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Keywords: | Self-diffusion coefficient Free volume Water clusters Positron annihilation NMR |
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