Molecular dynamics study of a polymeric reverse osmosis membrane
Journal of Physical Chemistry B, 113, 2009, 10177?10182
Edward Harder1, D. Eric Walters2, Yaroslav D. Bodnar3, Ron S. Faibish3 and Benoi?t Roux1
1Department of Biochemistry and Molecular Biology, Center for Integrative Science, University of Chicago, Illinois, 60637
2Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064
3Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois, 60439
In this paper, MD was applied to simulate the movement of water across a densely cross-linked aromatic polyamide membrane. Monomers were interconnected while following a heuristic distance criterion for cross-linking. The monomers used are metaphenyldiamine (MPD) and trimesoyl chloride (TMC): the basic components used for the synthesis of FT-30 polyamide through the Schotten-Baumann reaction. The generalized AMBER force field (GAFF) was used for the monomers. TMC and MPD were reacted forming amide linkages generated with ANTECHAMBER 1.27 and AM1-BCC partial charges. Membrane polymerization was carried out at constant volume and temperature. It was conducted as a stagewise series of interconnection processes among the monomers until the material was sufficiently dense; an example of a self-limiting phenomenon.
To determine if the model is realistically close to true membranes, bulk transport properties such as density and diffusivity were obtained using MD and compared to experimental values. The density of the dry membrane was first measured and the membrane was then solvated for the measurement of the diffusivity of water and the membrane's new density. TIP3P water model was used. The obtained water flux, 1.4 × 10?6 m/s was concluded to be fairly close to the experimental flux value of 7.7 × 10-6 m/s.
Thin film composite membranes made from polyamide are currently one of the most commonly used membranes for RO. MD simulation was used here as a way of characterizing the accuracy of a model for the complex cross-linking of the said non-porous membrane. Estimated properties obtained from MD can validate the heuristic used for polymer assembly if they are fairly close to experimentally-obtained values, which were concluded to be so.
John Matthew V. Cajudo