Effects of ions on the diffusion coefficient of water in carbon nanotubes
X Gao and TS Zhao and ZG Li, JOURNAL OF APPLIED PHYSICS, 116, 054311 (2014).
In this work, we investigate the ion effects on the diffusion of water in carbon nanotubes through molecular dynamics simulations. The diffusion coefficient of water molecules D-w in the presence of cations (Na+ and K+) and anions (F-, Cl-, and Br-) are calculated by changing the ion concentration. The dependence of Dw on the ion concentration is found highly nonlinear and distinct for different ions. For positively charged systems, as the ion concentration is varied, D-w assumes a maximum under the competition between the number and orientation changes of free OH bonds and the effects of ionic hydration. For negatively charged systems, however, D-w decreases monotonously with increasing ion concentration for F-. For Cl- and Br-, D-w reaches the minima at certain ion concentrations and then gently increases. The different behaviors of D-w in the presence of different anions are caused by the stability change of water hydrogen bonds due to ionic hydration. (C) 2014 AIP Publishing LLC.
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