Water Infiltration in ZSM-5 Zeolites: Effect of Pore Volume and Water Structure

This study investigates the infiltration of water in ZSM-5 zeolite crystals via molecular dynamics simulations and experiments. A zeolite nano-crystal is constructed in the simulations and is surrounded by water molecules which enter and saturate the pores. The average number of water molecules per unit cell of the zeolite is determined along with the radial distribution function of water inside the zeolites. A geometric approximation of the zeolite pores and intersections is proposed and verified. Partial charge on the zeolite atoms is found to be a crucial parameter which governs the water infiltration behavior. ZSM-5 zeolite crystals were also synthesized and water infiltration experiments were conducted using an Instron. The simulation and experimental findings are compared and discussed. The understanding gained from these studies will be important for the development of zeolite based reverse osmosis membranes for water desalination.

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Parametric Study on the Effect of Partial Charge on Water Infiltration Behavior in MFI Zeolites

Volume 10: Micro- and Nano-Systems Engineering and Packaging ◽

10.1115/imece2015-52997 ◽

2015 ◽

Author(s):

Geoffrey A. Vaartstra ◽

Tom Humplik ◽

Evelyn N. Wang ◽

Shalabh C. Maroo

Keyword(s):

Molecular Dynamics ◽

High Pressures ◽

Water Infiltration ◽

Water Molecules ◽

Partial Charge ◽

Mfi Zeolite ◽

Partial Charges ◽

Dynamics Simulations ◽

Mfi Zeolites ◽

Infiltration Behavior

This work analyzes the infiltration behavior of water into sub-nanometer MFI zeolite pores using molecular dynamics simulations. Infiltration simulations are run for a range of partial charge values on the zeolite atoms. Infiltration behavior is compared to partial charges to verify dependence and determine critical charge above which infiltration becomes severely inhibited even at high pressures. Attraction energy is calculated and correlated to the observed infiltration behavior. The critical partial charge of Si∼1.8 occurs when the water-zeolite interaction energy becomes stronger than water-water attraction due to which water molecules get stuck and infiltration is significantly reduced.

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Entropy Rules: Molecular Dynamics Simulations of Model Oligomers for Thermoresponsive Polymers

Entropy ◽

10.3390/e22101187 ◽

2020 ◽

Vol 22 (10) ◽

pp. 1187

Author(s):

Alexander Kantardjiev ◽

Petko M. Ivanov

Keyword(s):

Entropy Change ◽

Atomic Scale ◽

Solution Temperature ◽

Water Molecules ◽

Thermoresponsive Polymers ◽

Simulation Data ◽

Critical Solution Temperature ◽

Extended Conformation ◽

Dynamics Simulations ◽

Experimental Findings

We attempted to attain atomic-scale insights into the mechanism of the heat-induced phase transition of two thermoresponsive polymers containing amide groups, poly(N-isopropylacrylamide) (PNIPAM) and poly(2-isopropyl-2-oxazoline) (PIPOZ), and we succeeded in reproducing the existence of lower critical solution temperature (LCST). The simulation data are in accord with experimental findings. We found out that the entropy has an important contribution to the thermodynamics of the phase separation transition. Moreover, after decomposing further the entropy change to contributions from the solutes and from the solvent, it appeared out that the entropy of the solvent has the decisive share for the lowering of the free energy of the system when increasing the temperature above the LCST. Our conclusion is that the thermoresponsive behavior is driven by the entropy of the solvent. The water molecules structured around the functional groups of the polymer that are exposed to contact with the solvent in the extended conformation lower the enthalpy of the system, but at certain temperature the extended conformation of the polymer collapses as a result of dominating entropy gain from “released” water molecules. We stress also on the importance of using more than one reference molecule in the simulation box at the setup of the simulation.

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Water Structure on Mica Surfaces: Investigating the Effect of Cations

10.26434/chemrxiv.9851975.v1 ◽

2019 ◽

Author(s):

Jiarun Zhou ◽

Nurun Nahar Lata ◽

Sapna Sarupria ◽

will cantrell

Keyword(s):

Divalent Cations ◽

Water Structure ◽

Ice Nucleation ◽

Water Molecules ◽

Interfacial Water ◽

Ice Nucleation Protein ◽

Naturally Occurring ◽

Air Interface ◽

Bulk Structure ◽

Dynamics Simulations

We studied thin films of water at the mica-air interface using infrared spectroscopy and molecular dynamics simulations. We investigate the influence of ions on interfacial water by exchanging the naturally occurring K+ ion with H+/Na+, Ca2+, and Mg2+. The experiments do not show a difference in the bulk structure (i. e. in the infrared spectra), but indicate that water is more strongly attracted to the Mg2+ mica. The simulations reveal that the cation-water interactions significantly influence the microscopic arrangement of water on mica. Our results indicate that the divalent cations result in strong water-mica interactions, which leads to longer hydrogen bond lifetimes and larger hydrogen bonded clusters of interfacial water molecules. These results have implications for surface-mediated processes such as heterogeneous ice nucleation, protein assembly and catalysis.

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Liquid Water Confined in Cellulose with Variable Interfacial Hydrophilicity

Zeitschrift für Physikalische Chemie ◽

10.1515/zpch-2017-1011 ◽

2018 ◽

Vol 232 (7-8) ◽

pp. 989-1002 ◽

Cited By ~ 11

Author(s):

Tobias Watermann ◽

Daniel Sebastiani

Keyword(s):

Liquid Water ◽

Smooth Surface ◽

Water Structure ◽

Bulk Water ◽

Spatial Accessibility ◽

Water Molecules ◽

Crystal Water ◽

Coordination Numbers ◽

Interfacial Water Structure ◽

Dynamics Simulations

Abstract We investigate liquid water confined within nanoscale cellulose slabs by means of molecular dynamics simulations. Depending on the construction of the cellulose–water interface, two different surface structures with distinct levels of hydrophilicity are exposed to the water. The different philicities are reflected in the response of the water phase to this geometric confinement, both in terms of the density profile and in the strength of the aqueous hydrogen bonding network. At the smooth surface cut along the (010) axis of the cellulose crystal, water shows typical properties of a hydrophilic confinement: the density shows fluctuations that disappear further away from the wall, the water molecules orient themselves and the coordination numbers increases at the interface. As a consequence, the water becomes “harder” at the interface, with a considerably increased local ordering. At the zigzag-shaped surface along the (111) axis, the degree of hydrophilicity is reduced, and only small effects can be seen: the density shows weak fluctuations, and the orientation of the water molecules is closer to that of bulk water than to the smooth surface. The local coordination numbers remains constant over the whole confinement. Our work shows that the nature of the exposed cellulose interface has a strong influence on how the structure of adjacent water is modified. The different ways of surface construction yield distinct degrees of hydrophilicity and spatial accessibility regarding the hydrogen bond network, resulting in a notably different interfacial water structure.

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MOLECULAR DYNAMICS SIMULATIONS OF DMPC/DPPC MIXED BILAYERS

International Journal of Modern Physics C ◽

10.1142/s0129183107010267 ◽

2007 ◽

Vol 18 (01) ◽

pp. 73-89 ◽

Cited By ~ 5

Author(s):

ARMEN H. POGHOSYAN ◽

HRANT H. GHARABEKYAN ◽

ARAM A. SHAHINYAN

Keyword(s):

Md Simulation ◽

Orientational Order ◽

Hydrocarbon Chain ◽

Water Molecules ◽

Hydrocarbon Chains ◽

Racemic Mixtures ◽

Area Per Lipid ◽

Dynamics Simulations ◽

Experimental Findings ◽

Good Agreement

We have performed the atomistic MD simulation of dimyristoylphosphatidylcholine(DMPC)/dipalmitoylphosphatidylcholine(DPPC) mixed bilayers, consisting of various fraction of lipids, i.e., with fraction 0.25, 0.5 and 0.75 and hydration level 33 water molecules per lipid. The simulations were performed using NAMD code.The area per lipid, densities, orientational order parameters and tilt angle of hydrocarbon chain and also the interdigitation of chains were calculated. It has been established that the interdigitation degree of hydrocarbon chains is increased as the DPPC fraction is decreased. It has been also stated that the area per lipid value in case of racemic mixtures is about 0.72 nm2, which is in good agreement with experimental estimations. The hydrocarbon thickness is increased as the DPPC fraction increased. The DMPC/DPPC mixtures behave as almost ideally mixtures.The diffusion coefficients were also calculated and the results are in agreement with experimental findings.All the calculated parameters were compared with values obtained either from experimental data of DPPC or DMPC depending on the fraction of compound. The reason is that there are no experimental findings on DMPC/DPPC mixtures.

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Water Structure on Mica Surfaces: Investigating the Effect of Cations

10.26434/chemrxiv.9851975 ◽

2019 ◽

Author(s):

Jiarun Zhou ◽

Nurun Nahar Lata ◽

Sapna Sarupria ◽

will cantrell

Keyword(s):

Divalent Cations ◽

Water Structure ◽

Ice Nucleation ◽

Water Molecules ◽

Interfacial Water ◽

Ice Nucleation Protein ◽

Naturally Occurring ◽

Air Interface ◽

Bulk Structure ◽

Dynamics Simulations

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Numerical Study and Experimental Validation of Deformation of FCC CuAl Single Crystal Obtained by Additive Manufacturing

Metals ◽

10.3390/met11040582 ◽

2021 ◽

Vol 11 (4) ◽

pp. 582

Author(s):

Anton Y. Nikonov ◽

Andrey I. Dmitriev ◽

Dmitry V. Lychagin ◽

Lilia L. Lychagina ◽

Artem A. Bibko ◽

...

Keyword(s):

Single Crystal ◽

Numerical Study ◽

Strain Curve ◽

Aluminum Bronze ◽

Partial Dislocations ◽

Slip Planes ◽

Loaded Material ◽

Dislocation Movement ◽

Dynamics Simulations ◽

Experimental Findings

The importance of taking into account directional solidification of grains formed during 3D printing is determined by a substantial influence of their crystallographic orientation on the mechanical properties of a loaded material. This issue is studied in the present study using molecular dynamics simulations. The compression of an FCC single crystal of aluminum bronze was performed along the <111> axis. A Ni single crystal, which is characterized by higher stacking fault energy (SFE) than aluminum bronze, was also considered. It was found that the first dislocations started to move earlier in the material with lower SFE, in which the slip of two Shockley partials was observed. In the case of the material with higher SFE, the slip of a full dislocation occurred via successive splitting of its segments into partial dislocations. Regardless of the SFE value, the deformation was primarily occurred by means of the formation of dislocation complexes involved stair-rod dislocations and partial dislocations on adjacent slip planes. Hardening and softening segments of the calculated stress–strain curve were shown to correspond to the periods of hindering of dislocations at dislocation pileups and dislocation movement between them. The simulation results well agree with the experimental findings.

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Electrical Breakdown Mechanism of Transformer Oil with Water Impurity: Molecular Dynamics Simulations and First-Principles Calculations

Crystals ◽

10.3390/cryst11020123 ◽

2021 ◽

Vol 11 (2) ◽

pp. 123

Author(s):

Bin Cao ◽

Ji-Wei Dong ◽

Ming-He Chi

Keyword(s):

Molecular Dynamics ◽

Thermal Diffusion ◽

First Principles ◽

Electrical Breakdown ◽

Transformer Oil ◽

Water Molecules ◽

Conducting Channel ◽

Breakdown Mechanism ◽

Water Impurity ◽

Dynamics Simulations

Water impurity is the essential factor of reducing the insulation performance of transformer oil, which directly determines the operating safety and life of a transformer. Molecular dynamics simulations and first-principles electronic-structure calculations are employed to study the diffusion behavior of water molecules and the electrical breakdown mechanism of transformer oil containing water impurities. The molecular dynamics of an oil-water micro-system model demonstrates that the increase of aging acid concentration will exponentially expedite thermal diffusion of water molecules. Density of states (DOS) for a local region model of transformer oil containing water molecules indicates that water molecules can introduce unoccupied localized electron-states with energy levels close to the conduction band minimum of transformer oil, which makes water molecules capable of capturing electrons and transforming them into water ions during thermal diffusion. Subsequently, under a high electric field, water ions collide and impact on oil molecules to break the molecular chain of transformer oil, engendering carbonized components that introduce a conduction electronic-band in the band-gap of oil molecules as a manifestation of forming a conductive region in transformer oil. The conduction channel composed of carbonized components will be eventually formed, connecting two electrodes, with the carbonized components developing rapidly under the impact of water ions, based on which a large number of electron carriers will be produced similar to “avalanche” discharge, leading to an electrical breakdown of transformer oil insulation. The water impurity in oil, as the key factor for forming the carbonized conducting channel, initiates the electric breakdown process of transformer oil, which is dominated by thermal diffusion of water molecules. The increase of aging acid concentration will significantly promote the thermal diffusion of water impurities and the formation of an initial conducting channel, accounting for the degradation in dielectric strength of insulating oil containing water impurities after long-term operation of the transformer.

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Origin and control of ionic hydration patterns in nanopores

Communications Materials ◽

10.1038/s43246-021-00162-x ◽

2021 ◽

Vol 2 (1) ◽

Author(s):

Miraslau L. Barabash ◽

William A. T. Gibby ◽

Carlo Guardiani ◽

Alex Smolyanitsky ◽

Dmitry G. Luchinsky ◽

...

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulations ◽

Distribution Functions ◽

Water Molecules ◽

Surrounding Water ◽

Ionic Hydration ◽

Hydration Shells ◽

Water Layers ◽

Dynamics Simulations ◽

And Control

AbstractIn order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

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Optimal Relabeling of Water Molecules and Single-Molecule Entropy Estimation

Biophysica ◽

10.3390/biophysica1030021 ◽

2021 ◽

Vol 1 (3) ◽

pp. 279-296

Author(s):

Federico Fogolari ◽

Gennaro Esposito

Keyword(s):

Single Molecule ◽

Degrees Of Freedom ◽

Water Molecules ◽

Maximum Information ◽

Nearest Neighbours ◽

Biomolecular Simulations ◽

Solvent Molecules ◽

Solvation Entropy ◽

Dynamics Simulations ◽

Internal Degrees Of Freedom

Estimation of solvent entropy from equilibrium molecular dynamics simulations is a long-standing problem in statistical mechanics. In recent years, methods that estimate entropy using k-th nearest neighbours (kNN) have been applied to internal degrees of freedom in biomolecular simulations, and for the rigorous computation of positional-orientational entropy of one and two molecules. The mutual information expansion (MIE) and the maximum information spanning tree (MIST) methods were proposed and used to deal with a large number of non-independent degrees of freedom, providing estimates or bounds on the global entropy, thus complementing the kNN method. The application of the combination of such methods to solvent molecules appears problematic because of the indistinguishability of molecules and of their symmetric parts. All indistiguishable molecules span the same global conformational volume, making application of MIE and MIST methods difficult. Here, we address the problem of indistinguishability by relabeling water molecules in such a way that each water molecule spans only a local region throughout the simulation. Then, we work out approximations and show how to compute the single-molecule entropy for the system of relabeled molecules. The results suggest that relabeling water molecules is promising for computation of solvation entropy.

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