Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane

Gao,W, She,F, Zhang,J, Dumée,LF, He,L, Hodgson,PD and Kong,L 2015, Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane, Journal of Membrane Science, vol. 487, pp. 32-39, doi: 10.1016/j.memsci.2015.03.052.

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Title Understanding water and ion transport behaviour and permeability through poly(amide) thin film composite membrane
Author(s) Gao,WORCID iD for Gao,W orcid.org/0000-0002-7390-169X
She,FORCID iD for She,F orcid.org/0000-0001-8191-0820
Dumée,LFORCID iD for Dumée,LF orcid.org/0000-0002-0264-4024
Kong,LORCID iD for Kong,L orcid.org/0000-0001-6219-3897
Journal name Journal of Membrane Science
Volume number 487
Start page 32
End page 39
Publisher Elsevier
Publication date 2015-08
ISSN 0376-7388
Keyword(s) Free energy
Membrane desalination
Molecular dynamics
Poly(amide) thin film
Water diffusion
Science & Technology
Physical Sciences
Engineering, Chemical
Polymer Science
Summary Molecular dynamics (MD) together with the adaptive biasing force (ABF) and metadynamics free energy calculation methods was used to investigate the permeation properties of salt water through poly(amide) thin film composite reverse osmosis membranes. The thin films were generated by annealing an amorphous cell of poly(amide) chains through an MD method. The MD results showed they have typical structural properties of the active layer of thin film composite membranes and comparable water diffusivity (2.13×10-5cm2/s for the film with a density of 1.06g/cm3) and permeability (9.27×10-15cm3cm/cm2sPa) to experimental data. The simulations of water permeation through the films under different transmembrane pressures revealed the behaviours of water molecules in the thin films and the dynamic regimes of water permeation, including Brownian diffusion, flush and jump diffusion regimes. The intermolecular interactions of water and ions with poly(amide) chains showed a strong dependence on the local structure of films. The attraction between water and ploy(amide) molecules can be up to 8.5kcal/mol in dense polymer regions and 5kcal/mol in the pores of about 3nm. The ABF and metadynamics simulations produced the profiles of free energy potential of water and ions along the depth of the thin films, which provided important information for quantitatively determining the barrier energy required for water permeation and rejection of ions. The thin film with a density of 1.06g/cm3 and a thickness of 6nm offers a rejection to Na+ but a slight absorption of Cl- (0.25kcal/mol) at 0.3-0.4nm distance to its surface. Water molecules must overcome 63kcal/mol energy to move to the centre of the film. The dependences of the barrier energy and the water-polymer interaction energy on the local free volume size in the thin film were analysed. The simulations of water permeation under high transmembrane pressures showed a nonlinear response of the concentration and distribution of water molecules in the film to the imposed pressure. Compaction of the film segments close to the porous substrate and water congestion in dense regions significantly influenced the water permeation when the membrane was operated under pressures of more than 3.0MPa.
Language eng
DOI 10.1016/j.memsci.2015.03.052
Field of Research 090404 Membrane and Separation Technologies
090410 Water Treatment Processes
Socio Economic Objective 860604 Organic Industrial Chemicals (excl. Resins
HERDC Research category C1 Refereed article in a scholarly journal
Copyright notice ©2015, Elsevier
Persistent URL http://hdl.handle.net/10536/DRO/DU:30073856

Document type: Journal Article
Collections: Institute for Frontier Materials
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