Adsorption dynamics of polyatomic molecules on planar surfaces.

This is a comparative study of the adsorption dynamics of increasingly longer polyatomic molecules on a planar surface. We perform kinetic Monte Carlo simulations of the gas uptake to identify the molecular mechanisms and parameters that govern the evolution of the adsorbed film to its final equilibrium state. We also develop an analytical model for the adsorption dynamics of mono-atomic gases that demonstrates a direct correlation between the strength of the gas-gas interaction and the adsorption rate dependence with coverage.

Sorption Kinetics on Open Carbon Nanohorn Aggregates: The Effect of Molecular Diameter.

We present the results of a study of the kinetics of adsorption on aggregates of open carbon nanohorns using argon and CF₄ sorbates. We measured the equilibration times for each value of the sorbent loading along eight adsorption isotherms (four isotherms for each sorbate species). We found that: the equilibration times decrease as the sorbent loading (and the equilibrium pressure of the coexisting gas) increases, for a given temperature; and, that, for a given value of the sorbent loading, the equilibration times decrease with increasing temperature.

Equilibration processes during gas uptake inside narrow pores.

We analyze the adsorption kinetics of a gas in contact with the open ends of a narrow longitudinal pore, where gas transport along its interior occurs via single-file diffusion mechanisms. By implementing a Kinetic Monte Carlo simulation of the gas dynamics, we obtain the overall change in gas uptake inside the pore and the concentration profile of the adsorbed phase as the system evolves towards equilibrium. Typically, higher external pressure leads to faster kinetics as it happens for adsorption on open surfaces.

Adsorption kinetics of diatomic molecules.

The adsorption dynamics of diatomic molecules on solid surfaces is examined by using a Kinetic Monte Carlo algorithm. Equilibration times at increasing loadings are obtained, and explained based on the elementary processes that lead to the formation of the adsorbed film. The ability of the molecules to change their orientation accelerates the overall uptake and leads to competitive kinetic behaviour between the different orientations.

Dependence of single-walled carbon nanotube adsorption kinetics on temperature and binding energy.

We present results for the isothermal adsorption kinetics of methane, hydrogen, and tetrafluoromethane on closed-ended single-walled carbon nanotubes. In these experiments, we monitor the pressure decrease as a function of time as equilibrium is approached, after a dose of gas is added to the cell containing the nanotubes. The measurements were performed at different fractional coverages limited to the first layer.

CF4 on carbon nanotubes: physisorption on grooves and external surfaces.

We present the combined results of a computer simulation and adsorption isotherm investigation of CF4 films on purified HiPco nanotubes. The experimental measurements found two substeps in the adsorption data. The specific surface area of the sample and the coverage dependence of the isosteric heat of adsorption of the films were determined from the measurements.

Lattice-gas Monte Carlo study of adsorption in pores.

A lattice-gas model of adsorption inside cylindrical pores is evaluated with Monte Carlo simulations. The model incorporates two kinds of sites: (a line of) "axial" sites and surrounding "cylindrical shell" sites, in the ratio 1:7. The adsorption isotherms are calculated in either the grand canonical or canonical ensembles.

Ground state and thermal properties of a lattice gas on a cylindrical surface.

Adsorbed gases within, or outside of, carbon nanotubes may be analyzed with an approximate model of adsorption on lattice sites situated on a cylindrical surface. Using this model, the ground state energies of alternative lattice structures are calculated, assuming Lennard-Jones pair interactions between the particles. The resulting energy and equilibrium structure are nonanalytic functions of radius (R) because of commensuration effects associated with the cylindrical geometry.

Lattice model of gas condensation within nanopores.

We explore the thermodynamic behavior of gases adsorbed within a nanopore. The theoretical description employs a simple lattice gas model, with two species of site, expected to describe various regimes of adsorption and condensation behavior. The model includes four hypothetical phases: a cylindrical shell phase (S), in which the sites close to the cylindrical wall are occupied, an axial phase (A), in which sites along the cylinder's axis are occupied, a full phase (F), in which all sites are occupied, and an empty phase (E).

Simple model of capillary condensation in porous media.

We employ a simple model to describe the phase behavior of 4He and Ar in a hypothetical porous material consisting of a regular array of infinitely long, solid, parallel cylinders. We find that high porosity geometries exhibit two transitions: from vapor to film and from film to capillary condensed liquid. At low porosity, the film is replaced by a "necking" configuration, and for a range of intermediate porosity there are three transitions: from vapor to film, from film to necking and from necking to a capillary condensed phase.

Dilation-induced phases of gases absorbed within a bundle of carbon nanotubes.

A study is presented of the effects of gas (especially H2) absorption within the interstitial channels of a bundle of carbon nanotubes. The ground state of the system is determined by minimizing the total energy, which includes the molecules' interaction with the tubes, the intertube interaction, and the molecules' mutual interaction (which is screened by the tubes). The consequences of swelling include a reduced threshold pressure for gas uptake and a 2.