MD Analysis of Effect of Relative Humidity on Molecular Chain’s Network Structure of PEM

2016 ◽  
Vol 725 ◽  
pp. 238-242
Author(s):  
Isamu Riku ◽  
Keisuke Kawanishi ◽  
Koji Mimura
Keyword(s):  
Molecular Dynamics ◽  
Relative Humidity ◽  
Computational Model ◽  
Network Structure ◽  
Water Channel ◽  
High Density ◽  
Nafion Membrane ◽  
Water Molecules ◽  
Low Density ◽  
Density Of Water

To clarify the effect of relative humidity on molecular chain’s network structure, we at first employ Molecular Dynamics (MD) method to constitute the computational model for Nafion membrane, in which the water channel is artificially reproduced with an aggregation of water molecules. And then, relaxation calculation is performed and a relatively stable microstructure of Nafion membrane is derived. It is found that the regions of relatively low density of molecular chain’s network appear interchangeably together with those of relatively high density of water molecules.

scholarly journals Dynamic Properties of Water Confined in Graphene-Based Membrane: A Classical Molecular Dynamics Simulation Study

Membranes ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 165 ◽  
Author(s):  
One-Sun Lee
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Graphene Sheets ◽  
Water Molecules ◽  
Energy Profile ◽  
Confined Water ◽  
Graphene Surface ◽  
Dynamics Simulations ◽  
Density Of Water

We performed molecular dynamics simulations of water molecules inside a hydrophobic membrane composed of stacked graphene sheets. By decreasing the density of water molecules inside the membrane, we observed that water molecules form a droplet through a hydrogen bond with each other in the hydrophobic environment that stacked graphene sheets create. We found that the water droplet translates as a whole body rather than a dissipate. The translational diffusion coefficient along the graphene surface increases as the number of water molecules in the droplet decreases, because the bigger water droplet has a stronger van der Waals interaction with the graphene surface that hampers the translational motion. We also observed a longer hydrogen bond lifetime as the density of water decreased, because the hydrophobic environment limits the libration motion of the water molecules. We also calculated the reorientational correlation time of the water molecules, and we found that the rotational motion of confined water inside the membrane is anisotropic and the reorientational correlation time of confined water is slower than that of bulk water. In addition, we employed steered molecular dynamics simulations for guiding the target molecule, and measured the free energy profile of water and ion penetration through the interstice between graphene sheets. The free energy profile of penetration revealed that the optimum interlayer distance for desalination is ~10 Å, where the minimum distance for water penetration is 7 Å. With a 7 Å interlayer distance between the graphene sheets, water molecules are stabilized inside the interlayer space because of the van der Waals interaction with the graphene sheets where sodium and chloride ions suffer from a 3–8 kcal/mol energy barrier for penetration. We believe that our simulation results would be a significant contribution for designing a new graphene-based membrane for desalination.

Molecular Dynamics Study of Proton and Water Transport in Nafion Membrane

2013 ◽  
Author(s):  
Takuya Mabuchi ◽  
Takashi Tokumasu
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
Water Clusters ◽  
Nafion Membrane ◽  
Water Molecules ◽  
Static Structure ◽  
Hydration Level ◽  
Hydronium Ions ◽  
Structure Factors

Polymer electrolyte fuel cells (PEFCs) are highly expected as a next-generation power supply system due to the purity of its exhaust gas, its high power density and high efficiency. The polymer electrolyte membrane is a critical component for the performance of the PEFCs and it is important to understand the nanostructure in the membrane to enhance proton transport. We have performed an atomistic analysis of the vehicular transport of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane by systematically changing the hydration level which provides insights into a connection between the nanoscopic and mesoscopic structure of ion clusters and the dynamics of hydronium ions and water molecules in the hydrated Nafion membrane. In this study, classical molecular dynamics simulations are implemented using a model of Nafion membrane which is based on DREIDING force field and newly modified and validated by comparing the density, water diffusivity, and Nafion morphology with experimental data. The simulated final density after the annealing procedure agrees with experiment within 1.3 % for various water contents and the trends that density decreases with increasing hydration level are reproduced. In addition to determination of diffusion coefficients of solvent molecules as a function of hydration level (from λ = 1 up to λ = 18), we have also calculated radial distribution functions and static structure factors not only to clarify the structure of water molecules and hydronium ions around the first solvation shell of sulfonate groups but also to validate the mesoscopic periodic structure among water clusters. The diffusion coefficient of water molecules increases with increasing hydration level and is found to be in good agreement with experimental data. The diffusion coefficient of hydronium ions has showed that general trends in the experimental data are reproduced by the simulations although the classical models have the limitation of probing hydronium dynamics. The static structure factors of liquid molecules at low wave length provide insights into the periodic structure of the inter-water clusters. These results are consistent with the Gebel’s model based on small-angle X-ray scattering that considers the dry membrane to be made of isolated spherical ionic clusters of radius ∼7.5 Å that swell with increasing hydration.

scholarly journals Large-scale atomistic and quantum-mechanical simulations of a Nafion membrane: Morphology, proton solvation and charge transport

2013 ◽  
Vol 4 ◽  
pp. 567-587 ◽  
Author(s):  
Pavel V Komarov ◽  
Pavel G Khalatur ◽  
Alexei R Khokhlov
Keyword(s):  
Molecular Dynamics ◽  
Density Functional ◽  
Large Scale ◽  
Water Channel ◽  
Ion Association ◽  
Characteristic Size ◽  
Potential Of Mean Force ◽  
Nafion Membrane ◽  
Quantum Molecular Dynamics ◽  
Ion Conducting

Atomistic and first-principles molecular dynamics simulations are employed to investigate the structure formation in a hydrated Nafion membrane and the solvation and transport of protons in the water channel of the membrane. For the water/Nafion systems containing more than 4 million atoms, it is found that the observed microphase-segregated morphology can be classified as bicontinuous: both majority (hydrophobic) and minority (hydrophilic) subphases are 3D continuous and organized in an irregular ordered pattern, which is largely similar to that known for a bicontinuous double-diamond structure. The characteristic size of the connected hydrophilic channels is about 25–50 Å, depending on the water content. A thermodynamic decomposition of the potential of mean force and the calculated spectral densities of the hindered translational motions of cations reveal that ion association observed with decreasing temperature is largely an entropic effect related to the loss of low-frequency modes. Based on the results from the atomistic simulation of the morphology of Nafion, we developed a realistic model of ion-conducting hydrophilic channel within the Nafion membrane and studied it with quantum molecular dynamics. The extensive 120 ps-long density functional theory (DFT)-based simulations of charge migration in the 1200-atom model of the nanochannel consisting of Nafion chains and water molecules allowed us to observe the bimodality of the van Hove autocorrelation function, which provides the direct evidence of the Grotthuss bond-exchange (hopping) mechanism as a significant contributor to the proton conductivity.

FROZEN IODINE MOLECULES IN NANO-PORES OF ZEOLITE SINGLE CRYSTALS

2013 ◽  
Vol 27 (18) ◽  
pp. 1330014 ◽  
Author(s):  
DINGDI WANG ◽  
WENHAO GUO ◽  
SHENGWANG DU ◽  
Z. K. TANG
Keyword(s):  
Molecular Dynamics ◽  
Raman Spectroscopy ◽  
Optical Properties ◽  
Molecular Dynamics Simulation ◽  
Single Crystals ◽  
Iodine Atom ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Channel Switching ◽  
Density Of Water

We review the recent study of novel optical properties of iodine molecules trapped inside the nano-channels of single zeolite crystals. It has been verified by Raman spectroscopy and molecular dynamics simulation that there are two favorite orientations of iodine molecules inside the AlPO 4-11 (AEL) and AlPO 4-5 (AFI) crystal channels: "lying" along the channel direction or "standing" inside the channel. Switching between the "lying" and "standing" configurations of iodine molecules inside the AEL crystals can be controlled by varying the density of water molecules inside the crystal channels. For extremely low iodine-loaded samples, the frozen "standing" iodine molecules in AEL crystals were observed whose Raman linewidth is independent of temperature. We also show that the radius of iodine atom can be determined from the fading nature and the broadening characteristics of overtones in Raman spectra of confined iodine molecules.

Born-Oppenheimer molecular dynamics simulations on structures of high-density and low-density water: A comparison of the SCAN meta-GGA and PBE GGA functionals

2020 ◽  
Author(s):  
Mengli Li ◽  
Lu Chen ◽  
Lirong Gui ◽  
Shuo Cao ◽  
Di Liu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
High Density ◽  
Ab Initio Molecular Dynamics ◽  
Low Density ◽  
Dynamics Simulations

Using Born-Oppenheimer ab initio molecular dynamics (BOAIMD) simulations, the high-density water (HDW) and low-density water (LDW) structures based on SCAN meta-GGA are compared with those based on PBE GGA. Compared...

scholarly journals Polyamorphism and Two State Model in Liquid GeO\(_{2}\) under Compression: Insight from Visualization of Molecular Dynamics Data

2014 ◽  
Vol 24 (3S1) ◽  
pp. 95-98
Author(s):  
Nguyen Van Hong ◽  
Mai Thi Lan ◽  
Nguyen Thu Nhan
Keyword(s):  
Molecular Dynamics ◽  
Phase Region ◽  
High Density ◽  
State Model ◽  
Dynamics Simulation ◽  
Low Density ◽  
Wide Pressure Range ◽  
Simulation Results ◽  
Two State Model ◽  
Wide Pressure

The polyamorphism and two-state model based on the coordination number distribution in liquid GeO\(_{2}\) at 3200~K and in a wide pressure range are investigated by molecular dynamics simulation. Results show that the structure of liquid GeO\(_{2}\) mainly consists of GeO\(_{x}\) coordination units \((x=4,5,6)\) and OGe\(_{y}\) linkages \((y=2, 3)\). The distribution of OGe\(_{y}\) linkages in network structure is not uniform but tends to form clusters of OGe\(_{y}\). The cluster of OGe\(_{2}\) will form low-density phase region, conversely the cluster of OGe\(_{3}\) will form high-density phase region. In other word, under compression, in the liquid GeO\(_{2}\) coexist two states: low-density and high-density. The size of phase regions significantly depends on compression.

Quantitative defect studies in semiconductor TEM samples prepared by low angle ion milling

1995 ◽  
Vol 53 ◽  
pp. 512-513
Author(s):  
L. Mulestagno ◽  
J.C. Holzer ◽  
P. Fraundorf
Keyword(s):  
Sample Preparation ◽  
Milling Time ◽  
High Density ◽  
Low Density ◽  
Ion Milling ◽  
High Quality ◽  
Variable Angle ◽  
Major Disadvantage ◽  
Induced Defects

Due to the wealth of information, both analytical and structural that can be obtained from it TEM always has been a favorite tool for the analysis of process-induced defects in semiconductor wafers. The only major disadvantage has always been, that the volume under study in the TEM is relatively small, making it difficult to locate low density defects, and sample preparation is a somewhat lengthy procedure. This problem has been somewhat alleviated by the availability of efficient low angle milling.Using a PIPS® variable angle ion -mill, manufactured by Gatan, we have been consistently obtaining planar specimens with a high quality thin area in excess of 5 × 104 μm2 in about half an hour (milling time), which has made it possible to locate defects at lower densities, or, for defects of relatively high density, obtain information which is statistically more significant (table 1).

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