Polyatomic Adsorbates on Carbon Nanotube Bundles Aldo D. Migone, Southern Illinois University Carbondale, DMR Intellectual merit: Experimental - -We have found evidence that strongly suggests the existence of a phase transition (i.e. the type of change that occurs when ice becomes liquid water) for a one-molecule thick ethane film adsorbed on the surface of carbon nanotubes. Our results are the first ones to show the existence of sharp phase transitions on films adsorbed on nanotubes. -We have studied experimentally how long it takes for hydrocarbon molecules to adsorb on a nanotube substrate and form an equilibrium film. Equilibration times increase with increasing hydrocarbon chain length. Waiting times are longer for pentane (5 carbon-chain), followed by butane (four), propane (three), ethane (two) and methane (one). - We found that for longer molecules (pentane, butane), it takes longer for the film to accommodate and reach equilibrium the closer we are to covering the surface of the nanotubes completely (Fig. 1). The opposite is true for shorter chains (methane and ethane): it takes them shorter to accommodate the more the film covers the surface. These results are new and remain unexplained. Studying how fast gases adsorb on a material is relevant from a practical perspective because the speed with which a gas adsorbs on a substrate is one of the parameters that controls whether that material can be used for storing gas, or for separating gas mixtures in industrial processes. Theoretical - -We have conducted computer simulations for the adsorption of two-unit molecules (dimers) on a single chain of sites (see Fig. 2). The simulations show that for dimers the equilibration time decreases with increasing coverage coverage. This trend is similar to the one seen for spherical adsorbates. Figure 1 Kinetics of pentane adsorption on SWNTs. The graph shows how the pressure in the cell decreases as time elapses. The data shows how the time to equilibrate increases as the equilibrium pressure (and the surface coverage) increases. Figure 2 Schematic describing the computer simulation approach to the dimer calculation.

Polyatomic Adsorbates on Carbon Nanotube Bundles Aldo D. Migone, Southern Illinois University Carbondale, DMR Broader Impacts: - The research conducted for this project has provided the basis for the MS theses of three graduate students, and for the doctoral dissertation research for two other students. Two students have completed their MS degrees as a result of the work they carried out for this project. - We have established strong collaboration with the Porous Media group at the Universidad Nacional San Luis (Argentina) and with the experimental surface science group at the Theoretical and Applied Physical Chemistry Research Institute / Universidad Nacional de La Plata (Argentina). - Prof. Calbi visited National University of San Luis with her undergraduate student, Mr. J. Burde, in They presented talks on kinetics of gas adsorption on carbon nanotubes and adsorption of gases in interstitial channels of nanotubes bundles. They also started joint work in the theoretical study of the equilibrium and kinetic properties of multi-unit adsorbates, k-mers, on porous substrates. A k-mer is a simplified theoretical model version of a linear hydrocarbon (one with k C atoms). - Prof. Migone and his student, Ms. V. Krungleviciute, visited San Luis (in 2007 and 2008) and La Plata (in 2008) where they gave a series of talks on gas adsorption on various carbon nanomaterials. They conducted experiments on some of the setups available at UNSL and started exploring adsorption of gas mixtures and single-component adsorption at high pressures. As part of this interaction Profs. Migone and Calbi are developing a course covering all aspects of adsorption on novel nanostructures and on porous media. In 2008 Prof. Migone presented a series of lectures at UNSL on experimental techniques which will form part of this developing course. Prof. Migone at the National University of San Luis – Argentina discussing with Prof. Sapag (UNSL) and a student experiment s on a high-pressure adsorption setup. Preparing an acetone/dry ice (carbon dioxide) “slush” cryogenic bath for an adsorption experiment.