Peak Of Radial Distribution Function Research Articles

Micromechanical effects of substrate hardness on graphene nano-cutting quality

In the nanocutting process of graphene, the mechanism on the atomic scale of the effect of substrate hardness on the edge quality of graphene nanoribbons has not been thoroughly investigated. In this paper, we construct a diamond probe (radius of 5Å) to cut graphene (190Å × 113Å) models with different substrates (silicon/sapphire/silicon carbide), molecular dynamics simulations were used to study the effect of substrate hardness and cutting depth on the atomic structure of graphene nanoribbon edges by observing the atomic morphology, the number of C-C bonds, the radial distribution function and friction. The results show that during the nanoindentation stage, when graphene is in the critical damage state, the substrate with high hardness has high deformation strength, the substrate deformation is small, and graphene undergoes deformation is also small, but the force Fz on the probe, the critical graphene stress σz and the equivalent stress are all large, and the number of C atoms with CN=3 is large; At the nano-cutting stage, the breakage of C-C bonds and the generation of edge defects are caused by local stress concentration, and the graphene stress σxx along the x-direction has a clear directionality. With the same cutting depth (critical damage depth of silicon substrate), silicon substrate hardness is small, the graphene nanoribbon obtained has less number of circular defects generated at the edge, less total number of defective atoms, more number of CN=3 atoms, large peak of radial distribution function of graphene after cutting, and graphene integrity is better. The hardness of the silicon carbide substrate is large, and the number of C-C bond breaks in graphene during the cutting process is high. Each substrate is cut at its own critical damage depth, and the substrate hardness has no significant effect on the number of C-C bond breaks, the number of circular defects, the total number of defective atoms, and the number of CN=3 atoms in graphene. When the silicon substrate was used, the stable force of the probe is small, the edge structure of graphene has little impact, the edge effect obtained is good. The cutting depth and substrate hardness have little effect on the graphene temperature during the nano-cutting process. In this paper, the atomic structure of graphene edges after cutting is analysed and investigated on the atomic scale, and the above results are combined to provide theoretical guidance for obtaining efficient and high-quality and low-damage graphene nanoribbon cutting.

Morphological, Structural and Electronic properties of Zinc Oxide Nano Structures Deposited on ZnO Substrate Layer–A Theoretical Perspective

The work investigates the deposition of zinc and oxygen atoms on a Zinc terminated ZnO substrate, maintaining their stoichiometric ratio (O:Zn) at 0.8, under varying incident energies (0.5eV and 5eV) and temperatures (300K and 700K) using the ReaxFF potential in Molecular Dynamics (MD) simulation. The study explores the impact of deposition conditions on growth mechanisms, film morphology, and structural parameters such as Radial Distribution Function (RDF) and Coordination Number (CN). RDF analysis highlights disordered atomic arrangements and diverse bonding configurations within the film, with CN showing deviations from perfect crystalline ZnO, indicating non-uniform, non-crystalline, and nano behaviour. Post-heating the films to temperatures approaching the ZnO melting point results in enhanced crystallinity, as evidenced by distinct, dominant, and multiple RDF peaks. Density Functional Theory (DFT) approach of the deposited structures elucidates the formation of ZnO nanoclusters-(ZnO)3 and (ZnO)4 and investigates their electronic structure properties. DFT analysis of the post-heated films reveals the formation of ZnO monomers (ZnO), indicating an approaching crystalline behaviour, yet the films exhibit non-epitaxial and non-uniform characteristics. DFT calculations were instrumental in validating the observed structural behaviours in the deposited films. The study underscores the significance of stoichiometric ratio in film deposition and demonstrates the temperature-dependent evolution of structural properties towards crystallinity, shedding light on the intricate dynamics of ZnO film growth offering tailored control over film properties for enhanced performance in practical applications such as optoelectronics and gas sensing.

Effects of waste wood oil content on thermodynamic and structural properties of bio-asphalt and interactions between components: a molecular dynamic simulation study

ABSTRACT This study fully intends to elucidate the mechanism of waste wood oil (WWO) modifier content on the microscopic action of bio-asphalt by utilising molecular dynamics simulations. Molecular models of virgin asphalt and its components, WWO modifier, and bio-asphalt with different WWO contents were created and verified by the fluctuation parameters, radial distribution function (RDF), and thermodynamics parameters. In addition, the influence of WWO content on thermodynamic and structural properties of bio-asphalt and interactions between components was quantitatively evaluated through Hansen solubility parameter, intermolecular interaction energy, mean square displacement, RDF, and fraction of free volume. The simulation findings show that the compatibility of bio-asphalt is associated with the composition of the asphalt molecule and the compatibility ranking is not affected by the WWO content. In addition, the WWO modifier is most compatible with the resin and least with the saturate. The interaction energy between virgin asphalt and WWO and the particle migration in the asphalt models increases with increasing WWO content. Furthermore, the introduction of WWO increases the first RDF peak intensity of each asphalt component. An increase in WWO content does not change its own chemical composition. Moreover, the free volume of the system decreased as the WWO was added.

Structural and thermal analyses in semiconducting and metallic zigzag single-walled carbon nanotubes using molecular dynamics simulations.

Equilibrium molecular dynamics (EMD) simulations have been performed to investigate the structural analysis and thermal conductivity (λ) of semiconducting (8,0) and metallic (12,0) zigzag single-walled carbon nanotubes (SWCNTs) for varying ±γ(%) strains. For the first time, the present outcomes provide valuable insights into the relationship between the structural properties of zigzag SWCNTs and corresponding thermal behavior, which is essential for the development of high-performance nanocomposites. The radial distribution function (RDF) has been employed to assess the buckling and deformation understandings of the (8,0) and (12,0) SWCNTs for a wide range of temperature T(K) and varying ±γ(%) strains. The visualization of SWCNTs shows that the earlier buckling and deformation processes are observed for semiconducting SWCNTs as compared to metallic SWCNTs for high T(K) and it also evident through an abrupt increase in RDF peaks. The RDF and visualization analyses demonstrate that the (8,0) SWCNTs can more tunable under compressive than tensile strains, however, the (12,0) zigzag SWCNTs indicate an opposite trend and may tolerate more tensile than compressive strains. Investigations show that the tunable domain of ±γ(%) strains decreases from (-10%≤ γ ≤+19%) to (-5%≤ γ ≤+10%) for (8,0) SWCNTs and the buckling process shifts to lower ±γ(%) for (12,0) SWCNTs with increasing T(K). For intermediate-high T(K), the λ(T) of (12,0) SWCNTs is high but the (8,0) SWCNTs show certainly high λ(T) for low T(K). The present λ(T, ±γ) data are in reasonable agreement with parts of previous NEMD, GK-HNEMD data and experimental investigations with simulation results generally under predicting the λ(T, ±γ) by the ∼1% to ∼20%, regardless of the ±γ(%) strains, depending on T(K). Our simulation data significantly expand the strain range to -10% ≤ γ ≤ +19% for both zigzag SWCNTs, depending on temperature T(K). This extension of the range aims to establish a tunable regime and delve into the intrinsic characteristics of zigzag SWCNTs, building upon previous work.

Comparative study of cationic Nile blue and anionic methyl orange dyes adsorption in water on the (110) surface of metal chlorides by DFT and MD approaches

Computational studies using density functional theory (DFT) and molecular dynamics simulations (MD) provide a valuable way to evaluate the removal of dyes by different adsorbents. In this study, Nile blue (with a positive charge; NB+) and methyl orange (with a negative charge; MO−) were used to examine the adsorptive performance of metal chlorides MCl2 (where M = Mg, Mn, Zn or Ni) from water. The calculated gap energies of NB+ and MO− were 5.333 and 2.395 eV, respectively, suggesting that the NB+ molecule is more reactive, electrophilic and can adsorb strongly on the MCl2 surface compared to MO−. Frontier molecular orbitals, Mulliken charge and an electrostatic potential map were used to explain the redox reactive sites of the investigated molecules. In addition, possible donor–acceptor interactions of molecules were assessed by natural bond orbital analysis. The negative values of back-donation energy ΔEback-donation for both dyes reflected that back donation for both dyes was energetically favorable. Furthermore, the most stable energy configuration of NB+ and MO− adsorption on MCl2 was determined by MD simulations. These simulations showed that both dyes can be adsorbed onto the MCl2 (110) surface in a nearby horizontal position. The radial distribution function peak values for all systems occurred at distances greater than 3.5 Å, indicating that the dyes were physically adsorbed onto the MCl2 surfaces through van der Waals interactions. The negative values of adsorption energy for both studied dyes indicated spontaneity of the adsorption process. Furthermore, MD simulations revealed that the adsorption energies between NB+ and MCl2 were much higher than between MO− and MCl2.

Investigating medium range order in Mg-Al binary metallic glasses: Molecular dynamics approach

In this work, we used molecular dynamics (MD) simulations in order to investigate the Medium-Range Order (MRO) in Mg-Al binary metallic glasses (MGs). The embedded atom method (EAM) has been adopted to accurately model the interatomic interactions. Various techniques such as radial distribution function (RDF), coordination number (CN) analyses and Gaussian fitting have been mobilized to comprehensively study the impact of cooling rate, composition and mechanical solicitations, on the structural properties at the MRO level. Our results reveal that the 1-atom connection mode is consistently dominant across all cooling rates. Moreover, as the cooling rate increases in the Mg25Al75 binary MG, the abundance of the 4-atom and 2-atom connection modes increases, while the percentage of the 3-atom mode experiences a slight decrease. Furthermore, we investigate the influence of composition on the properties of MgxAl100-x alloys, demonstrating that the RDF peaks and connection modes are highly sensitive to variations in the Al concentration. Additionally, we explore the relationship between mechanical properties and connection modes during tensile deformation. The 3-atom connection mode exhibits superior hardness and stability, while the 4-atom and 2-atom connection modes offer increased flexibility. These significant findings enhance our understanding of MGs structural evolution, stability and deformation behavior. Ultimately, this knowledge facilitates the design and optimization of tailored MGs for advanced applications.

Molecular dynamics investigation on Widom line of binary mixtures of supercritical carbon dioxide containing noble gases

This work focuses on the effects of the addition of noble gases (Xe and Kr) at different concentrations on the thermodynamic properties and Widom line (WL) of supercritical carbon dioxide (S-CO2), as well as the microstructures of the binary mixture at different thermodynamic state points. Three thermodynamic properties (volume expansivity αp, isothermal compressibility κT, and isobaric heat capacity Cp) of CO2 + Xe and CO2 + Kr binary mixtures are investigated in the near-critical region (280–370 K, 8–14 MPa), and both of them significantly reduce the peaks of the three thermodynamic properties compared to pure CO2, and this effect enhances as the concentration of noble gases increases. The WL constructed by the maxima of the three thermodynamic properties of the CO2 + Xe binary mixture rotates clockwise around the critical point on the P-T plane as the concentration of Xe increases, while the same WL of the CO2 + Kr binary mixture shifts in the direction of temperature decrease on the P-T plane as the concentration of Xe increases. The Radial distribution function (RDF) of Xe and Kr in CO2 binary mixtures both exhibit significant first and blurry second peaks of RDF in the near-critical region consistent with pure CO2, which suggests the miscibility and homogeneity between CO2 and the two noble gases combined with visualization of the simulated mixture system.

Tuning structural and thermal conductivity of carbon nanotubes under strain effects

Equilibrium molecular dynamics (EMD) computations have been performed to estimate the thermal conductivity (λ) of armchair and chiral single-walled carbon nanotubes (SWCNTs) under the influence of varying axial compressive and tensile strains ±γ(%). For the first time, the present work provides new outcomes of structural behavior of SWCNTs linked through λ, considering the combinations of nanotube length (L), system temperature (T) and effects of varying ±γ(%). A radial distribution function (RDF) test has performed in order to investigate the structure analysis of armchair and chiral SWCNTs with different compressive (−1% – −10%) and tensile (+1% – +10%) strain sequences at the extreme L (= 100 Å and 1900 Å) and T (=300 K). The RDF and visualization tests indicate that both configurations are more tunable under tensile strain but the buckling processes of armchair SWCNTs are less evident as compared to chiral configurations. The simulation data shows that the λ(T, L) increases as L extends and it also confirmed through slight increase in RDF peaks, while the λ(T, L) of chiral SWCNTs is high compared to armchair SWCNTs for a complete range of T at L (= 100 Å and 1900 Å). However, the calculations indicate that the delta change in λ(T, L) of armchair SWCNTs is more than the chiral one, as expected. The simulation data demonstrates that the positions of the highest and lowest values of the thermal conductivity of the chiral SWCNTs shift to a longer L as compared to the armchair SWCNTs. The λ(T, L) of SWCNTs remains high for -γ(%) range at short L (=100 Å) due to less broaden shift in RDF peaks but slightly higher for +γ(%) range at longer L (=1900 Å) due to boarder shift in RDF peaks. Moreover, the present simulation results obtained from EMD approach are found to be in reasonable agreement with those obtained via the previous known numerical results.

Recycling waste engine oil as a viscosity reducer for asphalt rubber: an insight from molecular dynamics simulations and laboratory tests.

Traditional asphalt rubber (AR) has a high viscosity and poor fluidity, which makes its construction very difficult. Reducing viscosity has been identified as one of the effective way of solving these problems. Meanwhile, the mass production and improper discharge of waste engine oil (WEO) have a serious impact on the ecological environment, and its rational reuse needs to be addressed. In this paper, molecular models of AR and WEO-modified asphalt rubber (WEOMAR) was established by molecular dynamics (MD) simulations. The influence of WEO on asphalt component's behavior was studied by radial distribution function (RDF) and diffusion coefficient (D). Then, the microscopic mechanism of viscosity reduction was evaluated. Furthermore, the viscosity reduction behavior of WEO in AR was analyzed and verified by basic properties and low field nuclear magnetic resonance (LF-NMR) laboratory tests. The results showed that the RDF peak value of rubber molecules in WEOMAR is 14.07 higher than that of AR, at r = 2.16Å. The D of saturated and aromatic components in WEOMAR obviously increased by 140% and 67.9%, respectively. The light component molecules increased after adding WEO into AR. The rubber molecule reduces the contact with asphaltene and resin, and the viscosity of AR is significantly reduced, which is confirmed by the macro tests.

Atomistic insights into the effect of cooling rates on the structural and mechanical properties of Vanadium monatomic metallic glass

• Splitting in the second RDF peak is obtained for a cooling rate of 10 14 K/s. • Total energy decreases continuously for cooling rates of 5.10 13 K/s and 10 14 K/s. • Young...s modulus value of the V MG is large compared to the V in a liquid phase. Recently, metallic glasses have received much interest owing to their valuable and unique properties such as high corrosion resistance, high elasticity, fracture resistance, etc. In the present study, Molecular Dynamics (MD) simulation, based on semi-empirical potential described by the Embedded-Atom Method (EAM), was used to investigate the structural and mechanical properties of V-monoatomic Metallic glass. In order to analyze the behavior of this material, the radial distribution function (RDF) method and common neighbor analysis (CNA) were applied. The obtained results indicate a splitting in the second RDF peak with cooling rates of 10 14 K/s and 5.10 13 K/s. Furthermore, it was found that the total system energy decreases continuously when the high cooling rates of 5.10 13 K/s and 10 14 K/s are used, supporting the formation of Vanadium metallic glass (V MG). This latter one demonstrates a higher Young's modulus compared to the V-monatomic in the liquid phase.

Molecular dynamics simulation, DFT calculations and vibrational spectroscopic study of N[sbnd]H•••O bound dimer models for DL-β-phenylalanine and 3-amino-3-(4-chlorophenyl)propionic acid

Zwitterionic NH•••O bonded dimer structures have been proposed one each for DL-β-Phenylalanine and 3-Amino-3-(4-chlorophenyl)propionic acid. Stable zwitterionic monomer possessing NH3+ and COO¯ moieties in implicit aqueous solvation were computed at B3LYP/6-311++G** level and used for classical MD simulations. MD simulations yielded, among many NH•••O bonded transient dimer and trimer species, the two dimer structures with longest lifetime τ in water medium (τ = 111.67 ps for DL-β-Phenylalanine and 111.53 ps for 3-Amino-3-(4-chlorophenyl)propionic acid). The first peaks in radial distribution functions (RDF) confirmed the formation of NH•••O bonded dimer structures, one each for DL-β-Phenylalanine and 3-Amino-3-(4-chlorophenyl)propionic acid; the first minima determined the cut-off values for the inter-molecular H•••O distances. Further, the first minimum-solvation shell also indicated one zwitterionic dimer structure with 10 water molecules as solvent medium. Experimental IR frequencies due to the NH3+ and COO¯ moieties agree within 5% of the computed values for the dimer structures. Low-frequency Raman bands near 100–50 cm−1 are assigned to the torsional vibration modes of zwitterionic NH•••O bonded dimer structures. On the role of Chlorine with respect to all the molecular properties of 3-Amino-3-(4-chlorophenyl)propionic acid vs DL-β-Phenylalanine computed from NBO, AIM and NCI calculations, its influence is not substantial but discernible enough for gaining insights into the two NH•••O bonded zwitterionic dimer species.

Molecular dynamics simulation of the amorphization and alloying of a mechanically milled Fe-Cu system

The amorphization and alloying behavior of an Fe-Cu system were investigated by a three-dimensional molecular dynamics simulation. A repetitive process of attachment and compression of Fe and Cu boxes was applied for modeling the mechanical milling. Metallic glass and amorphous structures formed upon compression and relaxation, respectively. Short- and medium-range orders were found by normalizing all the radial distribution function peak positions to the first peak position. The values of the compressed box agreed well with those of undercooled melts, while the relaxed box values aligned with the glassy iron value. Voronoi polyhedron analysis revealed that the fraction of crystalline structure decreased and the icosahedra-like short-range order increased upon the processes. Fe and Cu atoms became uniformly distributed, and the fraction of Fe-Cu pairs increased upon the attachment processes. The molecular dynamics simulation with the repetitive processes can reveal the processes of amorphization and mixing in the Fe-Cu system.

Evaluation of SARS-CoV-2 main protease and inhibitor interactions using dihedral angle distributions and radial distribution function

In order to evaluate the interactions between a potential drug candidate like inhibitor N3 and the residues in substrate binding site of SARS-CoV-2 main protease (Mpro), we used molecular docking and dynamics simulations. The structural features describing the degrees of folding states of Mpro formed by beta-barrels and alpha-helices were analyzed by means of root mean square deviation, root mean square fluctuation, radius of gyration, residue velocity, H-bonding, dihedral angle distributions and radial distribution function. All of the residues forming ligand binding domain (LBD) of Mpro lie within the allowed region of the dihedral angle distributions as observed from the equilibrating best pose of Mpro-N3 system. Sharp peaks of radial distribution function (RDF) for H-bonding atom pairs (about 2 Å radial distance apart) describe the strong interactions between inhibitor and SARS-CoV-2 Mpro. During MD simulations, HSE163 has the lowest residue speed offering a sharp RDF peak whereas GLN192 has the highest residue speed resulting a flat RDF peak for the H-bonding atom pairs of Mpro-N3 system. Along with negative values of coulombic and Lenard-Jones energies, MM/PBSA free energy of binding contributed by the non-covalent interactions between Mpro and N3 has been obtained to be -19.45 ± 3.6 kcal/mol. These physical parameters demonstrate the binding nature of an inhibitor in Mpro-LBD. This study will be helpful in evaluating the drug candidates which are expected to inhibit the SARS-CoV-2 structural proteins.

Effect of Mg content on electronic structure, optical and structural properties of amorphous ZnO nanoparticles: A DFTB study

In this work, we perform a theoretical analysis of structural, electronic, and optical properties of pure and Mg-doped amorphous ZnO nanoparticles (a-ZnO NPs) using DFTB method. Our results show that Zn atoms are more preferential for Mg atoms than for O atoms because the number of MgZn bonds is greater than that of MgO. The rise in the content of Mg in a-ZnO NPs leads to an increase of Mg–Zn and MgO interactions. Mg atoms prefer to locate near the center of a-ZnO NP, but Zn and O atoms nearly preserve their positions which is compatible with radial distribution function peaks. The orbital energies display a decrease in the energy gap from 3.592 to 3.546 eV while increasing Mg content. The LUMO level is also significantly shifted to higher energies. The results also reveal that the performance of pure a-ZnO NP can be enhanced with a subsequent increase in Mg content.

On the structural changes and glass transition temperature relationship during the formation of Re-W metallic glasses

The search for advanced materials has been the main preoccupation of materials scientists for the past years. Binary Re-W metallic glasses (MGs) are very promising candidates for many applications requiring good mechanical proprieties. Molecular Dynamics (MD) simulations with the embedded atom method (EAM) potential have been devoted to investigate the behavior of these materials by exploring their local atomic structure by means of various techniques such as the radial distribution function (RDF), the Voronoi Tessellation Analysis (VTA) and the coordination number (CN). The results showed a splitting in the second peak of RDFs indicating the formation of Re-W metallic glasses. The VTA method showed that the <0,1,10,2> icosahedral Voronoi cluster is the major short-range unit in Re-W MGs. The icosahedral-like cluster abundance is proposed as a measure of vitrification which has been shown to be promoted by the increase of W content. The coordination number analysis showed the existence of transition from low- to high-coordinated atoms occurring at the glass transition temperature. These simulated structural properties were used mainly to study the glass transition temperature Tg using different methods, including the Wendt-Abraham method which is considered as a reference method. Essentially, we suggest the intersection between low- and high-coordinated atom populations to be a measure of Tg.

Molecular-level behavior of imidazolium-based ionic liquid mixtures

Understanding the molecular-level organization of anions and cations in a mixture of different ionic liquids (ILs) is challenging, but it can be very important for designing solvents and IL-based membrane materials. Here, we perform all-atom molecular dynamics (MD) simulations to understand the intermolecular interactions and structuring of both neat and mixed IL compositions containing 1-benzyl-3-methylimidazolium [ZMIM+], 1-butyl-3-methylimidazolium [BMIM+], bistriflimide [Tf2N−], and tetrafluoroborate [BF4−]. We observe very strong underlying molecular-level migrations in these mixtures, and this tends to mainly involve the anion species. As compared to the systems with a single anion, the mixed anions lead to large increases/decreases in the radial distribution function peak heights, whereas the cation mixing is relatively benign. The [BF4−] anions have a strong tendency to displace the [Tf2N−] anions in the mixtures, and this is seen with respect to both [BMIM+] and [ZMIM+].

Revisiting LiClO4 as an electrolyte for Li-ion battery: Effect of aggregation behavior on ion-pairing dynamics and conductance

A mixture of 0.5 M LiClO4 in 80% tetramethylsulfone (TMS) and 20% propylene carbonate (PC) was investigated through classical molecular dynamics simulations to understand properties that could make this a possible candidate for a better electrolyte for lithium-ion battery. The structural analysis through radial distribution function (RDF) reveals the strong interactions between Li+ and ClO4− ions, which increase with the increase in temperature. The interaction between the cation and the solvent molecules is found to be weaker than the cation-anion interactions. However, with an increase in temperature, the cation-TMS interactions decrease while the cation-PC interactions increase. There are prominent, sharp peaks in RDFs, which indicate an aggregating character of the ions in the system with pronounced effects in transport properties. The increase in temperature suggests a faster formation of these aggregates. The ions in this system show moderate ion transport and ionic conductivity. The obtained theoretical results were compared with the experimental data at the reported temperature. The value of correlated conductivity (0.24 mS cm−1) is in good agreement with the experimental (0.21 mS cm−1) results of 0.5 M LiClO4 in PC. Ionic conductivities were calculated for the various temperatures; it increases with increase in temperature. Conductivity calculated by either method shows Arrhenius behavior; the activation energy for ionic conduction is also discussed. From the dielectric calculations, it is observed that the dielectric constant of TMS decreases with an increase in temperature; this is the reason for the increased aggregating character of entities as the temperature increases. The model used in this study also provided values for the dielectric constant that was not very deviating from the experimental results. Understanding this feature, we also propose the concentration of electrolyte that shows enhanced conductivity by changing the TMS-PC proportions in the mixture.

Structural, Thermodynamic, and Transport Properties of Aqueous Reline and Ethaline Solutions from Molecular Dynamics Simulations.

Deep eutectic solvents (DESs) are a new generation of green solvents, which are considered an environmentally friendly alternative to ionic liquids and volatile organic compounds. The addition of controlled amounts of water to DESs has a significant effect on their microscopic structure and thus on their thermodynamic and transport properties. In this way, DESs can be modified, leading to solvents with improved characteristics. In this work, molecular dynamics (MD) simulations are performed to obtain a better understanding of the relation between the microscopic structure, molecular interactions, and thermophysical properties of aqueous reline and ethaline solutions at temperatures ranging from 303.15 to 363.15 K. For both reline and ethaline solutions, the hydrogen bond (HB) networks disappear with increasing mass fraction of water, and the intensity of radial distribution function (RDF) peaks decreases. For a mass fraction of water of 40%, most of the HBs between the compounds of reline and ethaline are broken, and DESs are fully dissolved in water. Consequently, a monotonic decrease in viscosities and an increase in self-diffusion coefficients are observed. Ionic conductivities show a nonmonotonic behavior with increasing water content. Up to 60% water mass fraction, the ionic conductivities increase with increasing water content. A further increase in the mass fraction of water decreases conductivities. For all studied systems, the HB network and the peaks of RDFs show relatively small changes for water mass fractions below 5% and beyond 40%. The MD results show that viscosities decrease with temperature, while diffusivities and ionic conductivities increase. The effect of the temperature on the structure of DES–water mixtures is negligible.

Transport property prediction and inhomogeneity analysis of supercritical n-Dodecane by molecular dynamics simulation

Predicting the transport properties of fuels in high-pressure conditions such as those for supercritical combustion has been a major challenge. In this study, molecular dynamics method of optimised potentials for liquid simulations force field is used to model the diesel fuel surrogate, i.e. n-Dodecane molecule. The Green-Kubo and Einstein methods are used to predict basic transport properties with conditions ranging from the high-pressure nozzle condition (150 MPa, 363 K) to the supercritical chamber environment (6 MPa, 900 K). The computed values agree well with experimental results in conditions with temperature and pressure far away from the critical point. But large discrepancies are observed in the neighborhood of the critical region due to density fluctuation and the critical divergence. The bulk viscosity of n-Dodecane is calculated and found to be hundreds of times greater than shear viscosity in supercritical conditions which cannot be ignored in computational fluid dynamics simulations. The inhomogeneity of supercritical fluids associated with the Widom and Frenkel lines is studied by mapping the loci of the extrema and “ridges” for compressibility coefficient, heat capacity, density fluctuation and velocity autocorrelation function on the P-T phase diagram. In addition, a new criterion is developed to distinguish inhomogeneity and structural transition of n-Dodecane into the “rigid-like”, “liquid-like” and “gas-like” fluids, by evaluating the decay of radial distribution function peak heights quantitatively.

Physicochemical Response of Gelatin in a Coulombic Soup of Monovalent Salt: A Molecular Simulation and Experimental Study.

The effect of salt on the static properties of aqueous solution of gelatin is studied by molecular dynamics simulation at pH = 1.2, 7, and 10. At the isoelectric point (pH = 7), a monotonic increase in size of the polymer is obtained with the addition of sodium chloride ions. In the positive polyelectrolyte regime (pH = 1.2), collapse of gelatin is observed with increase in salt concentration. In the negative polyelectrolyte regime, we observe an interesting collapse-reexpansion behavior. This is due to the screening of repulsion between the excess charges followed by the screening of attraction of oppositely charged ions as the salt concentration is increased. This mechanism is very different from the charge inversion mechanism which causes the reexpansion in the presence of multivalent ions. The location of salt concentration corresponding to the minimum size of the chain is comparable to the theoretical estimate. The shift in the peak of radial distribution function calculated between monomers and salt ions confirms this spatial reorganization. The predictions from the simulation are verified by dynamic light scattering(DLS) and small-angle X-ray scattering (SAXS) experiments. The size of the hydrodynamic "clusters" obtained from DLS confirms the simulation predictions. Persistence length of the gelatin is calculated from SAXS to get single chain statistics, which also agrees well with the simulation results.