Atomic scale friction between clean graphite surfaces

We investigate atomic scale friction between clean graphite surfaces by using molecular dynamics. The simulation reproduces atomic scale stick-slip motion and low frictional coefficient, both of which are observed in experiments using frictional force microscope. It is made clear that the microscopic origin of low frictional coefficients of graphite lies on the honeycomb structure in each layer, not only on the weak interlayer interaction as believed so far.Comment: 4 pages, 7 figure

Techniques in helical scanning, dynamic imaging and image segmentation for improved quantitative analysis with X-ray micro-CT

This paper reports on recent advances at the micro-computed tomography facility at the Australian National University. Since 2000 this facility has been a significant centre for developments in imaging hardware and associated software for image reconstruction, image analysis and image-based modelling. In 2010 a new instrument was constructed that utilises theoretically-exact image reconstruction based on helical scanning trajectories, allowing higher cone angles and thus better utilisation of the available X-ray flux. We discuss the technical hurdles that needed to be overcome to allow imaging with cone angles in excess of 60°. We also present dynamic tomography algorithms that enable the changes between one moment and the next to be reconstructed from a sparse set of projections, allowing higher speed imaging of time-varying samples. Researchers at the facility have also created a sizeable distributed-memory image analysis toolkit with capabilities ranging from tomographic image reconstruction to 3D shape characterisation. We show results from image registration and present some of the new imaging and experimental techniques that it enables. Finally, we discuss the crucial question of image segmentation and evaluate some recently proposed techniques for automated segmentation

Purification, Dispersion and Separation of Single Walled Carbon Nanotubes

In this thesis, the purification, dispersion and separation of Single Walled Carbon Nanotubes (SWNTs) are explored. The motivation for this work arose from the basic desire to understand and further develop the underlying chemistry of SWNTs, thus enabling the extraordinary properties of SWNTs to be used to their full potential. Achieving highly pure SWNT samples on which further chemistry can be undertaken is of critical importance; purification must be able to be performed in a reliable and repeatable manner. As such, a new method of SWNT purification was developed. This method introduced a new base washing step that removed a significant fraction of the impurities created during the standard acid reflux purification. This finding has implications for many existing reports on nanotube chemistry. Separation of SWNTs by their electronic properties is extremely important if SWNTs are to fulfil their potential in a wide range of applications, from optoelectronics to molecular sensing. In order to separate metallic and semiconducting SWNTs, two novel methods were developed, both of which are relatively cheap and easily scalable. First, SWNTs were reduced in liquid ammonia containing an alkali metal. The reduced tube salts were then spontaneously dissolved in dry solvents to form stable dispersions which were found to contain primarily metallic SWNTs; hence, separation was achieved. The second method investigated the separation of SWNTs reduced by electrochemical means. When a voltage was passed through a SWNT sample in a suitable electrolyte, SWNTs were reduced and therefore dissolved. These dissolved SWNTs were deposited as a thin carbon film, in which metallic SWNTs were found to preferentially present; once again, separation was achieved

Systematic pore-scale study of low salinity recovery from Berea sandstone analyzed by micro-CT

The low salinity effect in clay-rich outcrop sandstones is probed by micro-CT imaging and analysis. A set of eight Berea sandstone mini-plugs underwent primary drainage and aging in crude oil to a mixed-wet state, followed by spontaneous imbibition of high and low salinity brines and imaging of this sequence of prepared starting and endpoint states. Tomogram registration and analysis were used to determine the salinity-induced changes in oil volume, oil/rock and oil/brine interfacial areas, and oil/brine interfacial mean curvature. Pore-scale statistics were extracted to explore any local correlation between the low salinity effect and pore geometry/topology. The qualitative observations and quantitative analyses demonstrated that the small oil recovery by the low salinity effect corresponded to a slight shift towards water-wet.Financial support from the member companies of the Digital Core Consortium Wettability Satellite and Statoil are acknowledged

Role of carbonaceous fragments on the functionalization and electrochemistry of carbon materials

Carbonaceous fragments (CF) formed by acid treatment of carbon materials have important properties that are not completely understood. In this work, CF were produced by oxidation of CNT by using mineral acid followed by treatment with NaOH. The role of CF on CNT voltammetric properties was studied by using different materials: oxidized CNT (a-CNT), a-CNT refluxed in NaOH and neutralized with HCl (b-CNT), pristine CNT exposed to a CF suspension (c-CNT), and b-CNT exposed to a CF suspension (r-CNT). The extension of functionalization of these materials was evaluated by thermogravimetric analysis (TGA). The spectroscopic characterization (UV/Vis, fluorescence, FTIR, Raman and NMR) of CF indicates the presence of graphene-type conjugated aromatic rings with highly oxidized moieties. In this work we demonstrate that CF are responsible for the ameliorated voltammetric properties of oxidized CNT. Adsorption of CF on oxidized and non-oxidized CNT showed that CF provide active sites for hydroquinone (HQ) adsorption, enhancing current responses. The interaction of CF with carbon materials depended on both the surface oxidation degree and the surface roughness. Voltammograms from CF adsorbed on oxidized CNT indicate the presence of labile supramolecular structures with a voltammetric response typical of quinoid units. Carbon materials functionalized with CF displayed lower peak potentials and higher currents (30 to 180%) than the unmodified electrodes, demonstrating that CF is a promising material for sensors design.Thanks are due to FCT and COMPETE-QREN-EU for financial support: project PEst-/QUI/UI0686/2013 (Research Centre CQ/UM) and project PEst-C/CTM/ LA0025/2013 (IPC/I3N). RG and EC thank the FCT, POCH, and ESF for his Post- Doc (SFRH/BPD/86690/2012) and her Ph.D. grant (SFRH/BD/87214/2012), respectively.info:eu-repo/semantics/publishedVersio

Probing the charging mechanisms of carbon nanomaterial polyelectrolytes

Chemical charging of single-walled carbon nanotubes (SWCNTs) and graphenes to generate soluble salts shows great promise as a processing route for electronic applications, but raises fundamental questions. The reduction potentials of highly-charged nanocarbon polyelectrolyte ions were investigated by considering their chemical reactivity towards metal salts/complexes in forming metal nanoparticles. The redox activity, degree of functionalisation and charge utilisation were quantified via the relative metal nanoparticle content, established using thermogravimetric analysis (TGA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). The fundamental relationship between the intrinsic nanocarbon electronic density of states and Coulombic effects during charging is highlighted as an important area for future research

Added insight from image-based wettability characterization

Microtomographic rock and fluid imaging under in-situ conditions is applied for reservoir wettability characterization. The investigation entails careful sample preparation and cleaning of mini-plugs, operation with reservoir fluids, wettability restoration, centrifuge wettability testing cycles, repeated sample scanning and image analysis, parametrization of wettability and digital rocks simulation for input into reservoir modeling. The results are compared to conventional Amott testing performed in core laboratories. Determination of saturations from image analysis, instead of centrifuge production, allows the use of stock tank crude, rather than exchanged mineral oil. Doping of the synthetic formation water (here with 1 M sodium iodide) was applied for enhancement of the X-ray contrast. The digital imaging workflow offers insight on the liquid distributions from the plug scale down to the pore-scale, linked to applied pressure gradients and resulting pore fluid occupancies in the sequence of displacement states. An example is given with the investigation of a North-German oil field, where the image-based workflow led to a revised view of the reservoir conditions for spontaneous imbibition and drainage, and the overall wetting behavior