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Shahbabaei, M.,Kim, D. Elsevier 2016 Colloids and surfaces. A, Physicochemical and engi Vol.507 No.-
This research utilizes molecular dynamics (MD) simulations in order to study the effect of the length on water transport properties through the pore with an hourglass shape structure. While the narrowest section of the pore is kept constant, the length of the pore is increased in the range of 100-200A. The narrowest section allows water molecules to cross just in single-file configuration. It observed that flow decreases as the length increases unlike the water flux which increases with length, which attributes to the frictionless surface of the pore. In comparable with flux, the efficiency increases as the length increases. The increase of the diffusion coefficient and permeability together suggest that the entrance effect can be negligible as the length increases. It revealed that the friction force decreases with increasing the length. On the other hand, the displacement of water molecules from wall increases with length. These results together suggest that as the length increases the wall surface becomes frictionless.
Shahbabaei, Majid,Kim, Daejoong American Chemical Society 2017 The journal of physical chemistry. B, Condensed ma Vol.121 No.16
<P>In this study, molecular dynamics simulations are used to investigate water transport mechanisms through hourglass-shaped pore structure in nanoporous boron nitride (BN) and graphene multilayers. An increase in water flux is evidenced as the gap between the layers increases, reaching a maximum of 41 and 43 ns(-1) at d = 6 angstrom in BN and graphene multilayers, respectively. Moreover, the BN multilayer exhibits less flux compared to graphene due to large friction force and energy barrier. In BN, the friction force dramatically increases when the layers are strongly stacked (d = 3.5 A), whereas it would be independent of the layer separation when the layers are sufficiently spaced (d >= 5 angstrom). In contrast, it was shown that the friction force is independent of the layer spacing in graphene. 04 the other hand, water molecules across the BN exhibits larger energy barriers compared to graphene when the layers: are highly spaced at d = 8 angstrom. Consistent with the result reported for the flux, the axial diffusion coefficient of water molecules in graphene increases with layer spacing, reaching a maximum of 6.8 X 10(-5) cm(2)/s when the layers are spaced at a, 6 angstrom.</P>
Effect of hourglass-shaped nanopore length on osmotic water transport
Shahbabaei, M.,Kim, D. Elsevier Science Publishers [etc.] 2016 Chemical Physics Vol.477 No.-
<P>In the present research, molecular dynamic (MD) simulations are utilized in order to examine the water transport properties through hourglass-shaped pore structures with various lengths. The length elongates in a range of 100-200 angstrom, while the size of the narrowest diameter remains constant at 3 angstrom. The results show that the defect effect can be substantially diminished as the length increases, so that the fluctuations of the energy barrier reaches zero inside 200 angstrom pore structure, which is an indication of rapid increase of water transport rate. The flux increases with length, suggesting a reduction in hydrodynamic resistance, that water molecules are able to easily enter the pore. The axial diffusivity and permeability are increased once the length increments, which indicate a fast water transport. It is concluded that the thermal fluctuations of water molecules inside reservoir affect the motion of water molecules inside the pore as length decreases. (C) 2016 Published by Elsevier B.V.</P>
Simulation insight into water transport mechanisms through multilayer graphene-based membrane
Shahbabaei, Majid,Tang, Dai,Kim, Daejoong Elsevier 2017 Computational Materials Science Vol.128 No.-
<P><B>Abstract</B></P> <P>Although single-layer nanoporous graphene has proven to be effective as a reverse osmosis desalination membrane, multilayer nanoporous graphene (MNPG) is economically affordable to be synthesized. In this study, water transport through large cylindrical (LC) and small cylindrical (SC), as well as through large hourglass-shaped (LHGS) pore structures constructed by MNPG is investigated via molecular dynamics (MD) simulations. It was found that the number of occupancy states increases with increasing pressure in LC pore, whereas they decrease with increasing pressure in SC pore. At <I>P</I> =2katm, water molecules must overcome a very large free energy barrier in SC pore owing to large entrance effects, suggesting a dramatic reduction in net flux. The LHGS pore structure is suggested to be a more efficient design for achieving higher flux, compared to other structures.</P> <P>It was found that the hydrophilicity effect could nearly double the flux inside LHGS pore, owing to the strong hydrogen bonds. Moreover, the mean square displacement (MSD) profile in a hydrophilic pore shows larger displacement than a hydrophobic one, which facilitates water filling mechanism. It also indicated that the layers with hydrophilicity effect increase water concentration in the area close to the surface of the layers owing to strong hydrogen bonds. It is concluded that osmotic permeability of water molecules increases substantially inside hydrophilic LHGS pore.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>