Vacancy profile in reverse osmosis membranes studied by positron annihilation lifetime measurements and molecular dynamics simulations

16th International Conference on Positron Annihilation

Shimazu, A.^1 ; Goto, H.^2 ; Shintani, T.^1 ; Hirose, M.^1 ; Suzuki, R.^3 ; Kobayashi, Y.^3

Nitto Denko Corporation, 1-1-2, Shimohozumi, Ibaraki, Osaka 567-8680, Japan^1

Toyohashi University of Technology, Toyohashi, Aichi 441-8580, Japan^2

National Institute of Advanced Industrial Science and Technology, Tukuba-shi, Ibaraki 305-8568 and 8565, Japan^3

关键词: Diffusion behavior;    Molecular dynamics methods;    Molecular dynamics simulations;    Polyamide membranes;    Positron annihilation lifetime measurement;    Positron annihilation technique;    Slow positron beam;    Tokyo Institute of Technology;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/443/1/012050/pdf
DOI  :  10.1088/1742-6596/443/1/012050

来源: IOP

【 摘 要 】

The positron annihilation technique using a slow positron beam can be used for the study of the vacancy profiles in typical reverse osmosis (RO) membranes. In this study, the vacancy profile in the polyamide membrane that exhibits a high permselectivity between ions and water was studied using the positron annihilation technique and molecular dynamics simulations. Ortho-positronium (o-Ps) lifetimes in the surface region of the membranes were evaluated by using a slow positron beam. The diffusion behavior of Na+and water in the polyamides was simulated by molecular dynamics (MD) methods using the TSUBAME2 supercomputer at the Tokyo Institute of Technology and discussed with the vacancy profile probed by the o-Ps. The results suggested that the large hydration size of Na+compared to the vacancy size in the polyamides contributes to the increased diffusivity selectivity of water/Na+that is related to the NaCl desalination performance of the membrane. Both the hydration size of the ions and the vacancy size appeared to be significant parameters to discuss the diffusivity selectivity of water/ions in typical polyamide membranes.