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Milton W. Cole

Publications and source records attributed to Milton W. Cole.

35 records · Page 2Linked to original sources
arXiv2003

Universal anisotropic condensation transition of gases in nanotube bundles

Gases adsorbed within bundles of carbon nanotubes (inside of the nanotubes or in the interstitial channels between the tubes) exhibit a variety of phase transitions with the help of interactions between molecules in neighboring channels or tubes. Because the channels/tubes are widely separated, these transverse interactions are weaker than the (longitudinal) interactions within the same channel. The transition temperatures that result are therefore lower than those of typical two- or three-dimensional transitions of the same species of molecules. We discuss here the condensation transition of such a gas to form a liquid, expressing the transition behavior in universal form, where the reduced critical temperature T_c* is a universal function of the reduced transverse interaction.

cond-mat.soft↗
arXiv2003

Bose-Einstein Condensation of Molecular Hydrogen in Nanotube Bundles

We evaluate the effects of heterogeneity on the density of states of H$_2$ molecules inside interstitial channels within bundles of carbon nanotubes. As temperature (T) falls, the density increases within those tubes having the greatest binding energy. At T ~ 10 mK, the molecules undergo Bose-Einstein condensation, exhibiting a singular heat capacity.

cond-mat.soft↗
arXiv2003

Systematic model behavior of adsorption on flat surfaces

A low density film on a flat surface is described by an expansion involving the first four virial coefficients. The first coefficient (alone) yields the Henry's law regime, while the next three correct for the effects of interactions. The results permit exploration of the idea of universal adsorption behavior, which is compared with experimental data for a number of systems.

cond-mat.stat-mech↗
arXiv2003

Three-body interactions involving clusters and films

The three body (triple dipole) interaction of Axilrod, Teller and Muto (ATM) contributes 5 to 10 % of the total energy of condensed phases of inert elements. It is shown in this paper for clusters and films that a much larger or smaller ATM contribution can arise for other geometries or other atomic species. The ratio R of the three body interaction energy to the two body energy is evaluated for a wide variety of configurations. This ratio varies considerably with the geometry. For highly polarizable atoms in certain geometries, the magnitude of the three body energy is comparable to that of the two body energy and can be either attractive or repulsive. Systematic trends are established and explained.

cond-mat.soft↗
arXiv2003

Peas in a pod: quasi-one-dimensional C60 molecules in a nanotube

We evaluate the equation of state of the quasi-one-dimensional (1D) phase of C60 molecules in small carbon nanotubes, nicknamed ``peas in a pod''. The chemical potential and 1D pressure are evaluated as functions of the temperature and density, initially with the approximation of nearest neighbor interactions and classical statistical mechanics. Quantum corrections and long-range interaction corrections are discussed, as are the effects of interactions with neighboring peapods. Transition phenomena involving the 3D coupling are evaluated.

cond-mat.soft↗
arXiv2002

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. Specifically, as R varies, structural transitions occur between configurations differing in the "ring number", defined as the number of atoms located at a common value of the longitudinal coordinate (z). The thermodynamic behavior of this system is evaluated at finite temperatures, using a Hamiltonian with nearest-neighbor interactions. The resulting specific heat bears a qualitative resemblance to that of the one-dimensional Ising model.

cond-mat.soft↗
arXiv2002

Enhancing science education in the elementary schools

This article describes some collaborative activities of the authors, aimed at improving science education in elementary schools. These include curriculum enhancement, development of new apparatus (a wind tunnel), science-education web site contributions and production of a film about the physics of flight. The output of these projects is intended to be generally accessible or reproducible.

physics.ed-ph↗
arXiv2002

Dimensional crossover and quantum effects of gases adsorbed on nanotube bundles

Adsorption properties of several gases (Ne, CH4, Ar, Xe) on the external surface of a carbon nanotube bundle are investigated. Calculations are performed at low coverage and variable temperature, and for some temperatures as a function of coverage. Within a simple model (in the limit of very low coverage) we are able to study the evolution of the film's thermal properties from those of a one dimensional (1D) fluid to those of a 2D film. In addition, grand canonical Monte Carlo simulations are performed in order to identify a second layer groove phase, which occurs once a monolayer of atoms covers the external surface. We derive from the simulations the isosteric heat, compresibility and specific heat as a function of coverage. We evaluate alternative models in order to derive quantum corrections to the classical results. We compare our findings with those of recent adsorption experiments.

cond-mat.soft↗
arXiv2002

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). We obtain exact results at T=0 for the phase behavior, which is a function of the interactions present in any specific problem. We obtain the corresponding results at finite T from mean field theory. Finally, we examine the model's predicted phase behavior of some real gases adsorbed in nanopores.

cond-mat.stat-mech↗
arXiv2001

Evidence concerning Drying behavior of Ne near the Cs surface

Using density functional (DF) and Monte Carlo methods, we have studied the properties of Ne adsorbed on a Cs surface, focusing on the region at and near saturated vapor pressure (SVP). In the case of Ne/Rb, the experimental data of Hess, Sabatini and Chan are consistent with the calculations based on an ab initio fluid-substrate potential, while in the Ne/Cs case there is indication that the potential is approx 9% too deep. In that case, the calculations yield partial drying behavior consistent with the experimental finding of depressed fluid density near the surface, above SVP. However, we find no evidence of a drying transition, a result consistent with a mean field calculation of Ebner and Saam.

cond-mat.stat-mech↗
arXiv2001

Raman Spectroscopic Investigation of H2, HD, and D2 Physisorption on Ropes of Single-Walled, Carbon Nanotubes

We have observed the S- and Q-branch Raman spectra of H2, HD, and D2 adsorbed at 85K and pressures up to 8 atm on single-walled, carbon nanotubes (SWNT). Comparative data for H2 on graphite and C60 were also collected. For each adsorbate, we observed a small shift in the Q-branch frequencies relative to the gas-phase values. To aid in interpreting this result, we constructed an H2-surface potential, including van der Waals and electrostatic terms. Computed shifts based on this potential are in good agreement with our data.

cond-mat.soft↗
arXiv2001

Condensed phases of gases inside nanotube bundles

An overview is presented of the various phases predicted to occur when gases are absorbed within a bundle of carbon nanotubes. The behavior may be characterized by an effective dimensionality, which depends on the species and the temperature. Small molecules are strongly attracted to the interstitial channels between tubes. There, they undergo transitions between ordered and disordered quasi-one dimensional (1D) phases. Both small and large molecules display 1D and /or 2D phase behavior when adsorbed within the nanotubes, depending on the species and thermodynamic conditions. Finally, molecules adsorbed on the external surface of the bundle exhibit 1D behavior (striped phases), which crosses over to 2D behavior (monolayer film) and eventually 3D behavior (thick film) as the coverage is increased. The various phases exhibit a wide variety of thermal and other properties that we discuss here.

cond-mat.soft↗
arXiv2000

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 inter-tube interaction, and the molecules' mutual interaction (which is screened by the tubes). The consequences of swelling include a significant increase in the gas uptake and a 3 per cent increase in the tubes' breathing mode frecuency.

cond-mat.soft↗
arXiv2000

Many-body interactions among adsorbed atoms and molecules within carbon nanotubes and in free space

This paper assesses the importance of three-body triple dipole interactions for quasi-one dimensional phases of He, Ne, H_2, Ar, Kr and Xe confined within interstitial channels or on the external surfaces of nanotube bundles. We find the substrate-mediated contribution to be substantial: for interstitial H_2 the well depth of the effective pair potential is reduced to approximately one half of its value in free space. We carry out ab initio calculations on linear and equilateral configurations of H_2 trimer and find that overlap interactions do not greatly change the DDD interaction in the linear configuration when the spacing is greater than about 3 A. However, the DDD interaction alone is clearly insufficient for the triangular configurations studied.

cond-mat.mtrl-sci↗
arXiv1999

Helium mixtures in nanotube bundles

An analogue to Raoult's law is determined for the case of a 3He-4He mixture adsorbed in the interstitial channels of a bundle of carbon nanotubes. Unlike the case of He mixtures in other environments, the ratio of the partial pressures of the coexisting vapor is found to be a simple function of the ratio of concentrations within the nanotube bundle.

cond-mat.stat-mech↗
arXiv1999

Atoms in nanotubes: small dimensions and variable dimensionality

Newly discovered carbon nanotubes provide an environment in which small atoms move relatively freely. An assembly of such atoms provides a realization of a quasi-one dimensional system which is an ideal testing ground for concepts and mathematics of statistical physics.

cond-mat.stat-mech↗