Carbon-doped metal oxide interfacial nanofilms for ultrafast and precise separation of molecules.

Membranes with molecular-sized, high-density nanopores, which are stable under industrially relevant conditions, are needed to decrease energy consumption for separations. Interfacial polymerization has demonstrated its potential for large-scale production of organic membranes, such as polyamide desalination membranes. We report an analogous ultrafast interfacial process to generate inorganic, nanoporous carbon-doped metal oxide (CDTO) nanofilms for precise molecular separation.

Viscoelastic bandgap in multilayers of inorganic-organic nanolayer interfaces.

Incorporating molecular nanolayers (MNLs) at inorganic interfaces offers promise for reaping unusual enhancements in fracture energy, thermal and electrical transport. Here, we reveal that multilayering MNL-bonded inorganic interfaces can result in viscoelastic damping bandgaps. Molecular dynamics simulations of Au/octanedithiol MNL/Au multilayers reveal high-damping-loss frequency bands at 33 ≤ ν ≤ 77 GHz and 278 ≤ ν ≤ 833 GHz separated by a low-loss bandgap 77 ≤ ν ≤ 278 GHz region.

Investigating the validity of Schrage relationships for water using molecular dynamics simulations.

Recently, molecular dynamics (MD) simulations were utilized to show that Schrage theory predicts evaporation/condensation mass fluxes with good accuracy in the case of monoatomic and non-polar molecular fluids. Here, we examine if they are equally accurate for molecular polar fluids, such as water. In particular, using molecular dynamics (MD) simulations, we study the steady state evaporation/condensation processes of water in a one-dimensional heat-pipe geometry to ascertain the validity of Schrage relationships.

Multifold pressure-induced increase of electric conductivity in LiFeVPO glass.

We investigated the impact of high pressure and high-temperature annealing on lithium-vanadium-iron-phosphate (LiFeVPO) glass materials, proposed for the use in cathodes for high-performance batteries. The treatment was carried out below the glass transition temperature (T ≈ 483 °C) at P = 1 GPa pressure, in an argon atmosphere. It led to the multifold electrical conductivity increase.

Stochasticity in materials structure, properties, and processing-A review.

We review the concept of stochasticity-i.e., unpredictable or uncontrolled fluctuations in structure, chemistry, or kinetic processes-in materials.

Gibbs Adsorption Impact on a Nanodroplet Shape: Modification of Young-Laplace Equation.

We present an efficient technique for the evaluation of the Gibbs adsorption of a liquid on a solid substrate. The behavior of a water nanodroplet on a silicon surface is simulated with molecular dynamics. An external field with varying strength is applied on the system to tune the solid-liquid interfacial contact area.

Molecular simulation of steady-state evaporation and condensation in the presence of a non-condensable gas.

Using molecular dynamics simulations, we study evaporation and condensation of fluid Ar in the presence of a non-condensable Ne gas in a nanochannel. The evaporation and condensation are driven by the temperature difference, ΔT, between the evaporating and condensing liquid surfaces. The steady-state evaporation and condensation fluxes (J) are also affected by the Ne concentration, ρ, and the nanochannel length.

Nonlinear Electron-Lattice Interactions in a Wurtzite Semiconductor Enabled via Strongly Correlated Oxide.

With VO , a classic strongly correlated oxide material, a model semiconductor CdS is stretched and its electron-lattice interaction in a nonlinear manner is modulated. Optical spectroscopy is applied to probe the electronic band structure-associated parameters which is explained by the theoretical prediction based on k·p method and microscopy study. The research provides a new avenue on dynamic straining engineering.

Continuum and molecular-dynamics simulation of nanodroplet collisions.

The extent to which the continuum treatment holds in binary droplet collisions is examined in the present work by using a continuum-based implicit surface capturing strategy (volume-of-fluid coupled to Navier-Stokes) and a molecular dynamics methodology. The droplet pairs are arranged in a head-on-collision configuration with an initial separation distance of 5.3 nm and a velocity of 3 ms^{-1}.

Modeling high-temperature diffusion of gases in micro and mesoporous amorphous carbon.

In this work, we study diffusion of gases in porous amorphous carbon at high temperatures using equilibrium molecular dynamics simulations. Microporous and mesoporous carbon structures are computationally generated using liquid quench method and reactive force fields. Motivated by the need to understand high temperature diffusivity of light weight gases like H2, O2, H2O, and CO in amorphous carbon, we investigate the diffusion behavior as function of two important parameters: (a) the pore size and (b) the concentration of diffusing gases.

Slip length crossover on a graphene surface.

Using equilibrium and non-equilibrium molecular dynamics simulations, we study the flow of argon fluid above the critical temperature in a planar nanochannel delimited by graphene walls. We observe that, as a function of pressure, the slip length first decreases due to the decreasing mean free path of gas molecules, reaches the minimum value when the pressure is close to the critical pressure, and then increases with further increase in pressure. We demonstrate that the slip length increase at high pressures is due to the fact that the viscosity of fluid increases much faster with pressure than the friction coefficient between the fluid and the graphene.

Molecular dynamics investigation of nanoscale cavitation dynamics.

We use molecular dynamics simulations to investigate the cavitation dynamics around intensely heated solid nanoparticles immersed in a model Lennard-Jones fluid. Specifically, we study the temporal evolution of vapor nanobubbles that form around the solid nanoparticles heated over ps time scale and provide a detail description of the following vapor formation and collapse. For 8 nm diameter nanoparticles we observe the formation of vapor bubbles when the liquid temperature 0.

Thermal transport across a substrate-thin-film interface: effects of film thickness and surface roughness.

Using molecular dynamics simulations and a model AlN-GaN interface, we demonstrate that the interfacial thermal resistance R(K) (Kapitza resistance) between a substrate and thin film depends on the thickness of the film and the film surface roughness when the phonon mean free path is larger than film thickness. In particular, when the film (external) surface is atomistically smooth, phonons transmitted from the substrate can travel ballistically in the thin film, be scattered specularly at the surface, and return to the substrate without energy transfer. If the external surface scatters phonons diffusely, which is characteristic of rough surfaces, R(K) is independent of film thickness and is the same as R(K) that characterizes smooth surfaces in the limit of large film thickness.

Thermal resistance at an interface between a crystal and its melt.

Non-equilibrium molecular dynamics simulations are used to determine interfacial thermal resistance (Kapitza resistance) between a crystal and its melt for three materials including Ar, H2O, and C8H18 (octane). The simulation results show that the Kapitza resistance at a crystal-melt interface is very small and thus has a negligible effect on thermal transport across the crystal-melt interface. The underlying origins of this behavior are the very good vibrational property match between the two materials forming the interface and good interfacial bonding.

Curvature induced phase stability of an intensely heated liquid.

We use non-equilibrium molecular dynamics simulations to study the heat transfer around intensely heated solid nanoparticles immersed in a model Lennard-Jones fluid. We focus our studies on the role of the nanoparticle curvature on the liquid phase stability under steady-state heating. For small nanoparticles we observe a stable liquid phase near the nanoparticle surface, which can be at a temperature well above the boiling point.

Liquid phase stability under an extreme temperature gradient.

Using nonequilibrium molecular dynamics simulations, we subject bulk liquid to a very high-temperature gradient and observe a stable liquid phase with a local temperature well above the boiling point. Also, under this high-temperature gradient, the vapor phase exhibits condensation into a liquid at a temperature higher than the saturation temperature, indicating that the observed liquid stability is not caused by nucleation barrier kinetics. We show that, assuming local thermal equilibrium, the phase change can be understood from the thermodynamic analysis.

Equilibrium and nonequilibrium molecular dynamics simulations of thermal conductance at solid-gas interfaces.

The thermal conductance at solid-gas interfaces with different interfacial bonding strengths is calculated through Green-Kubo equilibrium molecular dynamics (EMD) simulations. Due to the finite size of the simulation system, the long-time integral of the time correlation function of heat power across the solid-gas interface exhibits an exponential decay, which contains the information on interfacial thermal conductance. If an adsorbed gas layer is formed on the solid surface, it is found that the solid-gas interface needs to be defined at a plane outside the adsorbed layer so as to obtain the correct result from the Green-Kubo formula.

Bonding-induced thermal conductance enhancement at inorganic heterointerfaces using nanomolecular monolayers.

Manipulating interfacial thermal transport is important for many technologies including nanoelectronics, solid-state lighting, energy generation and nanocomposites. Here, we demonstrate the use of a strongly bonding organic nanomolecular monolayer (NML) at model metal/dielectric interfaces to obtain up to a fourfold increase in the interfacial thermal conductance, to values as high as 430 MW m(-2) K(-1) in the copper-silica system. We also show that the approach of using an NML can be implemented to tune the interfacial thermal conductance in other materials systems.

Viscosity calculation of a nanoparticle suspension confined in nanochannels.

The kinetic properties of the pressure-driven Poiseuille flow in nanochannels with and without nanoparticles were studied with a nonequilibrium molecular dynamics simulation. To allow the fluid to dissipate heat, the boundary was kept at a constant temperature. Pure fluid simulations were taken as references and also used to study the fluid-wall interfacial interaction effects.

Heat localization for targeted tumor treatment with nanoscale near-infrared radiation absorbers.

Focusing heat delivery while minimizing collateral damage to normal tissues is essential for successful nanoparticle-mediated laser-induced thermal cancer therapy. We present thermal maps obtained via magnetic resonance imaging characterizing laser heating of a phantom tissue containing a multiwalled carbon nanotube inclusion. The data demonstrate that heating continuously over tens of seconds leads to poor localization (∼ 0.

Thermal conductivity of carbon nanotube cross-bar structures.

We use non-equilibrium molecular dynamics (NEMD) to compute the thermal conductivity (κ) of orthogonally ordered cross-bar structures of single-walled carbon nanotubes. Such structures exhibit extremely low thermal conductivity in the range of 0.02-0.

Heat transfer from nanoparticles: a corresponding state analysis.

In this contribution, we study situations in which nanoparticles in a fluid are strongly heated, generating high heat fluxes. This situation is relevant to experiments in which a fluid is locally heated by using selective absorption of radiation by solid particles. We first study this situation for different types of molecular interactions, using models for gold particles suspended in octane and in water.

How wetting and adhesion affect thermal conductance of a range of hydrophobic to hydrophilic aqueous interfaces.

We quantify the strength of interfacial thermal coupling at water-solid interfaces over a broad range of surface chemistries from hydrophobic to hydrophilic using molecular simulations. We show that the Kapitza conductance is proportional to the work of adhesion-a wetting property of that interface-enabling the use of thermal transport measurements as probes of the molecular environment and bonding at an interface. Excellent agreement with experiments on similar systems [Z.

Turning carbon nanotubes from exceptional heat conductors into insulators.

Thermal conductivity (kappa) of isolated carbon nanotubes (CNTs) is higher than the kappa of diamond; however, in this Letter we show that the kappa of a packed bed of three-dimensional random networks of single and multiwall CNTs is smaller than that of thermally insulating amorphous polymers. The thermoelectric power (Sigma) of the random network of CNTs was also measured. The Sigma of a single wall nanotube network is very similar to that of isolated nanotubes and, in contrast with kappa, Sigma shows a strong dependence on the tube diameter.

Critical heat flux around strongly heated nanoparticles.

We study heat transfer from a heated nanoparticle into surrounding fluid using molecular dynamics simulations. We show that the fluid next to the nanoparticle can be heated well above its boiling point without a phase change. Under increasing nanoparticle temperature, the heat flux saturates, which is in sharp contrast with the case of flat interfaces, where a critical heat flux is observed followed by development of a vapor layer and heat flux drop.