Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes
Lee, J, Doherty, CM, Hill, AJ and Kentish, SE (2013) Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes Journal of Membrane Science, 425. pp. 217-226.
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Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane's salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a commercial Dow Filmtec SW30 membrane and 188×1019 per gram for an aromatic polyamide material prepared in house. The activation energy for diffusion of water through the active layer of SW30 was also evaluated and found to be 6.95 kcal/mol, lower than the heat of liquefaction of water. This suggests that water does not permeate as individual molecules in the vapour state, but rather as clusters of water molecules. The free volume cavity size in the active layer as a function of moisture uptake was also investigated and the results were explained using a pore filling and pore swelling mechanism. This study sheds light on the mechanisms of water entry into the active layer, water transport through the active layer, and the corresponding response of the polymer chains, thereby giving critical insight for the development of more novel systems.
|Subjects :||Chemical and Process Engineering|
|Divisions :||Faculty of Engineering and Physical Sciences > Chemical and Process Engineering|
|Date :||1 January 2013|
|Identification Number :||https://doi.org/10.1016/j.memsci.2012.08.054|
|Copyright Disclaimer :||Copyright © 2012 Elsevier B.V.|
|Uncontrolled Keywords :||Science & Technology, Technology, Physical Sciences, Engineering, Chemical, Polymer Science, Engineering, ENGINEERING, CHEMICAL, POLYMER SCIENCE, Polyamide, Clustering, Water vapour, Permeation, PALS, FILM-COMPOSITE MEMBRANES, NANOFILTRATION MEMBRANES, TRANSPORT-PROPERTIES, FUNCTIONAL-GROUPS, GLASS-TRANSITION, SALT TRANSPORT, ION-TRANSPORT, RO MEMBRANES, NF MEMBRANES, ANNIHILATION|
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|Additional Information :||Item not available from this repository|
|Depositing User :||Symplectic Elements|
|Date Deposited :||19 Jul 2016 15:18|
|Last Modified :||19 Jul 2016 15:18|
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