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Phase changes associated with the boiling of cryogenic liquids are interesting phenomena. In the present study, liquid nitrogen, which has applications in microelectronics, semiconductors, and the space sector, has been considered as a representative cryogenic fluid. The boiling of liquid nitrogen was investigated at different lengths and time scales. At the micro level, classical molecular dynamics (MD) based simulations were performed to understand various facets of boiling, considering a film of liquid nitrogen on a solid surface. For macroscale study, the route of computational fluid dynamics (CFD) has been adopted. For accurately tracking the dynamic interface, coupled level set volume of fluid approach (CLSVOF) has been implemented. CFD results show the formation of vapour bubbles in liquid nitrogen at different degrees of wall superheats. Temporal variation of heat flux has been evaluated. Finally, the results obtained from MD and CFD simulations have been compared. [ABSTRACT FROM AUTHOR]

Evaporation of a sessile droplet on a hot solid substrate is an important problem in fluid mechanics. It is relevant to theoretical issues in heat transfer as well as several practical applications. This study investigates the spreading and evaporation of a nanoscale water droplet on a solid platinum surface. The major objective was to analyze the effect of an external electric field on these phenomena. Varying the intensity and direction of the external electric field, a series of molecular dynamics simulations were carried out to understand these phenomena at a molecular level. The results reveal that a horizontal electric field assists in droplet spreading, whereas a vertical electric field enhances the rate of evaporation for a certain range of field intensities. It also shows that the substrate temperature plays an important role in such processes. It is seen that the effect of an external electric field on droplet evaporation becomes significant at an intermediate range of surface temperatures and this effect is not clearly visible for either very high or very low range of surface temperatures. [ABSTRACT FROM AUTHOR]

Grand-canonical transition-matrix Monte Carlo and histogram reweighting techniques are used herein to study the vapor-liquid coexistence properties of two-dimensional (2D) flexible oligomers with varying chain lengths (m = 1-8). The phase diagrams of the various 2D oligomers follow the correspondence state (CS) principle, akin to the behavior observed for bulk oligomers. The 2D critical density is not influenced by the oligomer chain length, which contrasts with the observation for the bulk oligomers. Line tension, calculated using Binder's formalism, in the reduced plot is found to be independent of chain length in contrast to the 3D behavior. The dynamical properties of 2D fluids are evaluated using molecular dynamics simulations, and the velocity and pressure autocorrelation functions are investigated using Green-Kubo (GK) relations to yield the diffusion and viscosity. The viscosity determined from 2D non-equilibrium molecular dynamics simulation is compared with the viscosity estimated from the GK relations. The GK relations prove to be reliable and efficient for the calculation of 2D transport properties. Normal diffusive regions are identified in dense oligomeric fluid systems. The influence of molecular size on the diffusivity and viscosity is found to be diminished at specific CS points for the 2D oligomers considered herein. In contrast, the viscosity and diffusion of the 3D bulk fluid, at a reduced temperature and density, are strongly dependent on the molecular size at the same CS points. Furthermore, the viscosity increases and the diffusion decreases multifold in the 2D system relative to those in the 3D system, at the CS points. [ABSTRACT FROM AUTHOR]

Four novel pyrazine derivatives namely 2-aminopyrazine (AP), 2-amino-5-bromopyrazine (ABP), 3-amino pyrazine-2-thiol (APT) and 3-amino-6-bromopyrazine-2-thiol (ABPT) are investigated for their possible utilization as corrosion inhibitors by computational chemistry using density functional theory (DFT) and molecular dynamics (MD) simulation. Organic molecules (AP and ABP) along with two other similar organic framework (APT and ABPT) having an additional –SH group have been thoroughly investigated as corrosion inhibitors by means of theoretical investigation (DFT and MD simulation) with a vision that they can perform better. Their corrosion inhibition property have been calculated by several energy parameters like E HOMO , E LUMO , energy gap (Δ E ), electronegativity ( χ ), softness ( S ) and fraction of electron transferred from inhibitor molecule to metallic atom (Δ N ). Local reactivity of these molecules has been studied through Fukui indices. Significantly, DFT and MD simulation results are in well agreement with experimental outcomes for AP and ABP. Moreover the theoretical results show that –SH based pyrazine derivatives i.e. ; APT and ABPT, are even better potential candidate as corrosion resistant. Theoretical outcome reflects that introduction of –SH group will result betterment towards inhibition property. [ABSTRACT FROM AUTHOR]

Transitions from spinodal to pattern-guided dewetting of a bilayer of ultrathin films (<10 nm) confined between a pair of patterned surfaces have been explored employing molecular dynamic (MD) simulations. The physical or chemical defects of different sizes and shapes are decorated on the confining substrates by either removal or addition of multiple layers of similar or dissimilar atoms. The simulations are performed to identify the transition from spinodal pathway to the heterogeneous nucleation route, with the variation in the size of the substrate patterns. The MD simulations reveal the limits beyond which the defects can guide the dewetting to generate ordered patterns of nanoscopic size and periodicity. Comparing the results obtained from the MD simulations with the more widely employed continuum dynamics approach highlights the importance of the MD approach in quantitatively analyzing the dynamics of the dewetting of ultrathin films. The study demonstrates that the pattern-guided dewetting of confined bilayers can lead to ordered holes, droplets, and stripes with size and periodicity less than 10 nm, which are yet to be realized experimentally and can be of significance for a number of future applications. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) is a powerful tool for calculating several thermo-physical properties of wide range of materials. In this study, the diffusivities (D) of two widely used long chain molecules MHA and ODT are calculated at various temperatures using MD simulations coupled with Einstein relationship. Four different kinds of forcefields COMPASS, UFF, CVFF and PCFF are employed in the MD simulation and the results are compared. Diffusivity values are evaluated in a humid environment in presence of water molecules. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations have been conducted to understand the mechanism for bubble formation on a platinum substrate with particular emphasis on the surface texture. Liquid Argon, that follows the model of Lennard–Jones fluids, is the fluid of interest. The nano-sized bubbles are formed under different degree of superheat and surface conditions. The bubble nucleation and vapor film formation show dependence on the degree of superheat and solid–liquid interfacial wettability. A bubble does not form easily on a non-wetting surface. It is easy to nucleate a bubble on a smooth surface for higher degree of superheats. The hydrophilic surfaces provide favorable conditions for bubble nucleation and formation of vapor films. [Copyright &y& Elsevier]

Self-organized interfacial instabilities of an ultrathin bilayer confined between a pair of rigid surfaces is explored. The bilayers are classified based on the macroscopic dewetting behaviors of the liquid films sandwiched between a pair of confining surfaces having surface energy higher or lower than the liquid films. Linear and nonlinear analyses employing the governing equations originating from the continuum description together with molecular dynamics (MD) simulations unveil the salient spatiotemporal features of the dewetting process. The study uncovers that, under the destabilizing influence of the intermolecular interactions, the interface of a confined bilayer can deform into interesting embedded and encapsulated patterns with nanoscale periodicity. The continuum and MD simulations collectively show the detailed route to dewetting starting from the formation of holes in the early stage, their growth to achieve equilibrium contact angle at the intermediate phase, and then to evolve into the equilibrium morphologies at the later stage. Examples are shown where the length and the time scales of the simulated nanostructures from both the continuum and MD approaches are found to agree with the same obtained from the linear stability analysis. We also highlight the deviations that are observed in the continuum and MD approaches. The study confirms that the reduced stabilizing interfacial tension at the liquid-liquid interface together with enhanced intermolecular interaction because of the thinness of the layers can be an alternative strategy for pattern miniaturization exploiting the instabilities of a thin confined bilayer. Further, the study shows that use of topographical patterns on the bounding surfaces can impose periodic order to the holes, droplets, columns, and channels, which can find important applications in the diverse areas of nanotechnology. [ABSTRACT FROM AUTHOR]

Abstract: We present the equilibrium and dynamical properties of liquid sodium (Na) and lithium (Li), based on embedded atom models, using molecular dynamics simulations. In particular, we present vapor–liquid equilibria, critical properties, diffusivity, shear viscosity and excess entropy of liquid Na and Li. Critical temperatures obtained in the current work are 2462K and 5649K for Na and Li, respectively. On the other hand, critical density for Na is 0.3493g/cm3 and that for Li is 0.1553g/cm3. Critical pressures based on the exiting EAM models for Na and Li are 113bar and 1686bar, respectively. The relation of excess entropy and dynamical properties is examined in the framework of existing scaling laws. We observed an exponential nature between the dimensionless scaled diffusion constant and the approximate excess entropy for liquid Na and Li, as also observed for other liquid metals. [Copyright &y& Elsevier]

• Dynamics of ionic nanodroplets are investigated in external electric field. • The study includes evaporation and spreading at various surface temperatures. • The condition of varying temperature is modulated by the external electric field. • The effects of ionic droplets result in nanobridge/ nanocolumn under electric field. Effect of external electric field and surface temperature on the dynamics of a sessile ionic nanodroplet has been investigated using classical molecular dynamics (MD) simulations. The study investigates the spreading, evaporation and deformation behavior of a salt-water nanodroplet on a solid Pt surface in the presence and absence of external electric field. Varying the intensity and direction of the external electric field, a series of MD simulations were carried out considering a moderate concentration of ionic solution to understand these phenomena at molecular level. In the presence of salt ions, effect of hydration becomes more dominant which resists the deformation of the nanodroplet. It was also found that vertical electric field leads to the formation of nanobridge/column like structures beyond some critical field intensities. In addition to the electro-evaporation, the present study probes the effect of surface temperature on the evaporation and spreading process of the sessile ionic nanodroplet. [ABSTRACT FROM AUTHOR]

[Display omitted] • Molecular rearrangement inside an ionic nanodroplet in the presence of external electric field is studied using molecular dynamics simulations. • Effect of ion concentration on the structure of hydration shell is investigated. • Effect of electric field as well as ion concentrations on mean square displacement (MSD), drift velocity, mobility, and ion-water interaction energy are discussed. • Effect of solid substrate on the structural and dynamic properties of the nanodroplet is explored. This work deploys the molecular dynamics simulations to study the effect of an external electric field on the structural and dynamic properties of a sessile ionic nano-droplet. The results show that the presence of the ions at different concentrations causes significant deformations in the hydration shells. Such deformations resemble the effect of high pressure on water molecules. Due to the disintegration of the droplet under the influence of high intensity electric fields, the drift velocities and mobilities of the sodium and chlorine ions exhibit a decreasing trend in the presence of the solid substrate which is not observed in free droplets. The change in the ion-water interaction energy increases with the increasing electric field intensity. This implies an underlying reduction in the strength of ionic hydration. The presence of the Pt surface enhances the ion-water and water-water interactions. [ABSTRACT FROM AUTHOR]