Paper title: Molecular dynamics simulations of the interactions of potential foulant molecules and a reverse osmosis membrane
Journal: J. Mater. Chem., 2012, 22, 175

Author/s: Zak E. Hughes* and Julian D. Gale
-Nanochemistry Research Institute, Department of Chemistry, Curtin University, P.O. Box U1987, Perth, WA, 6845, Australia
-zak@ivec.org

Summary: 
The authors used molecular dynamics (MD) simulations combined with umbrella sampling methods to understand fouling of RO membranes. By constructing a fully atomistic model of a polyamide (PA) RO membrane and creating models for three different foulants, they were able to simulate the interactions between the membrane and the foulants.

The three foulants used in the study are glucose, phenol and oxygen gas. Glucose and phenol were chosen as the representatives for organic foulants because they have relatively simple structures and they are the building blocks for other more complicated organic structures. Meanwhile, oxygen, an inorganic foulant, was chosen because like other inorganic foulants, it is found to influence the properties of the PA membrane and it interacts with humic substances. 

Different simulations were run; varying the number of foulant molecules, concentration of saline solution, location of foulant and duration of production. The simulations were able to obtain the diffusion coefficients of water, oxygen, phenol, glucose, sodium and chloride in solution and in membrane. They were compared to experimental results. Aside from observing the movement of particles in the system, the authors were also able to determine radial distribution functions, free energy profiles, density profiles and binding strength of the foulants at different conditions. They were contrasted with each other and with experimental data.

But despite having numerous data and being able to draw many conclusions about the membrane-foulant interactions, the authors mentioned that these were still insufficient to differentiate which phenomena are foulant-induced and which are intrinsic membrane fluctuations.

Contribution and application:
Understanding fouling mechanism during SWRO is very important for the improvement of the process efficiency. This paper has shown the starting point for characterization of foulants and fouling mechanism through molecular dynamics simulations. Based on this paper, further studies may be made using foulants of higher complexities than the three used here. In addition, upgrades in the models may be made to determine more detailed explanations of fouling.



By: Hannah Ebro
hannah@gist.ac.kr