Molecular Dynamics Study of a Polymeric Reverse Osmosis Membrane
Authors: Edward Harder,1 D. Eric Walters,2 Yaroslav D. Bodnar,3 Ron S. Faibish,*,3 and Beno?t Roux*,1
1Department of Biochemistry and Molecular Biology, Center for Integrative Science, University of Chicago, Illinois, 60637, Chicago
2Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064
3Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois, 60439
In this paper, the synthesis of polymeric FT-30 polyamide membrane using molecular dynamics has been described. The monomers for the reaction are trimesoyl chloride (TMC) and m-phenylenediamine (MPD). The topology and parameter files were written using AmberTools package for molecular dynamics using generalized amber force filed (GAFF). The partial atomic charges on both the monomers were computed using ANTECHAMBER 1.27 with AM1-BCC partial charges. 250 monomers of TMC and 250 of MPD were randomly scattered in a periodic box with dimensions double than the size of the monomers. The simulation and construction of membrane was performed in CHARMM molecular dynamics package.
The simulation was carried out in four steps. In each step, 1000 simulation steps were carried out followed by energy minimization of the system. After each step, a heuristic approach was used to make polyamide bonds between nitrogen of MPD and carbon of the carbonyl group of TMC. In first step, the bonds were made when the nitrogen and carbon were at a distance of less than 3.5 ?. In the second step, this distance criterion was changed to the range 3.5 ? < r < 6.0 ?, while this criterion was relaxed to a distance of more than 6.0 ? in the third step. The relaxation of distance criterion was due to decrease in the rate of reaction.
This model represents the close approximation to the realistic RO membrane. The cross links were developed using heuristic approach. A table of amide bond order after each stage is shown in Table 1 while a figure of the four stages of polymerization are shown in Figure 1.
Reviewed by: Aamir Alaud Din