A First Assessment of Carbon Nanotubes Grown on Oil-Well Cement via Chemical Vapor Deposition.

In this study, carbon nanotubes (CNTs) were synthesized on an oil-well cement substrate using the chemical vapor deposition (CVD) method. The effect of synthesis process on cement was investigated in depth. In this regard, FE-SEM, RAMAN and X-Ray spectroscopy were used to characterize the cement before and after the synthesis process to reveal the modifications to the cementitious matrix and some unique morphological features of CNTs.

Towards highly stable aqueous dispersions of multi-walled carbon nanotubes: the effect of oxygen plasma functionalization.

In order to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in aqueous media, their surface functionalization was carried out in O2-fed low-pressure plasmas. Differently from what can be found in the literature of this field, homogeneous functionalization was achieved by generating the plasma inside vials containing the nanotube powders properly stirred. Experimental parameters, such as input power, treatment time and pressure, were varied to investigate their influence on the process efficiency. A detailed characterization of the plasma treated nanotubes, dry and in aqueous suspension, was carried out with a multi-diagnostic analytical approach, to evaluate their surface chemical properties, morphology, structural integrity and stability in the colloidal state. The plasma grafting of polar ionizable (e.g. acid) groups has been proved to successfully limit the agglomeration of MWCNTs and to produce nanotubes suspensions that are stable for one month and more in water.

Stimuli-responsive cement-reinforced rubber.

In this work, we report the successful development of a cement-rubber reactive composite with reversible mechanical properties. Initially, the composite behaves like rubber containing inert filler, but when exposed to water, it increases in volume and reaches a stiffness that is intermediate between that of hydrogenated nitrile butadiene rubber (HNBR) and hydrated cement, while maintaining a relatively large ductility characteristic of rubber. After drying, the modulus increases even further up to 400 MPa. Wet/drying cycles prove that the elastic modulus can reversibly change between 150 and 400 MPa. Utilizing attenuated total reflection Fourier transform infrared spectroscopy), we demonstrate that the high pH produced by the hydration of cement triggers the hydrolysis of the rubber nitrile groups into carboxylate anions. Thus, the salt bridges, generated between the carboxylate anions of the elastomer and the cations of the filler, are responsible for the reversible variations in volume and elastic modulus of the composite as a consequence of environmental moisture exposure. These results reveal that cement nanoparticles can successfully be used to accomplish a twofold task: (a) achieve an original postpolymerization modification that allows one to work with carboxylate HNBR (HXNBR) not obtained by direct copolymerization of carboxylate monomers with butadiene, and (b) synthesize a stimuli-responsive polymeric composite. This new type of material, having an ideal behavior for sealing application, could be used as an alternative to cement for oil field zonal isolation applications.

Compression behaviour of thick vertically aligned carbon nanotube blocks.

Blocks of vertically aligned multiwall carbon nanotubes were prepared by thermal chemical vapor deposition starting from camphor and ferrocene precursors. The blocks, having a thickness of approximately 2 mm and composed of nanotubes with diameter ranging between 30 and 80 nm, were submitted to compression tests. The results were analyzed accordingly with a simple model consisting in a parallel array of nanotubes under compression and bending suffering microscopic instability and compaction. The model mostly fits the experimental stress-strain curves, with a small deviation attributed to dissipative phenomena, such as frictional forces and nanotube wall breakage.

A sensitive and practical fluorimetric test for CNT acidic site determination.

A sensitive and practical colorimetric test for oxidized carbon nanotubes (CNTs) is described. The assay is based on direct labeling with the commercially available fluorescent dye thionin acetate (THA). This strategy offers the possibility for quantitation of acidic sites in a very fast and easy way.

High-temperature annealing effects on multiwalled carbon nanotubes: electronic structure, field emission and magnetic behaviors.

This work elucidates the effects of high-temperature annealing on the microscopic and electronic structure of multiwalled carbon nanotubes (MWCNTs) using high-resolution transmission electron microscopy, micro-Raman spectroscopy, X-ray diffraction, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES), respectively. The field emission and magnetization behaviors are also presented. The results of annealing are as follows: (1) MWCNTs tend to align in the form of small fringes along their length, promote graphitization and be stable in air, (2) XANES indicates an enhancement in oxygen content on the sample, implying that it can be adopted for sensing and storing oxygen gas, (3) the electron field emission current density (J) is enhanced and the turn-on electric field (E(TOE)) reduced, suggesting potential use in field emission displays and as electron sources in microwave tube amplifiers and (4) as-grown MWCNTs with embedded iron nanoparticles exhibits significantly higher coercivity approximately 750 Oe than its bulk counterpart (Fe(bulk) approximately 0.9 Oe), suggesting its potential use as low-dimensional high-density magnetic recording media.

Gas chromatography study of reagent degradation during chemical vapor deposition of carbon nanotubes.

The high temperature decomposition of three types of hydrocarbons, such as ethanol, camphor and cyclohexanol has been studied in order to determine the role played by the molecular structure of the precursor during the formation of carbon nanotubes (CNTs) catalyzed by ferrocene. This investigation will help in identifying the properties of the carbon precursor crucial to obtain the highest CNT selectivity and quality. A gas chromatography mass spectrometry (GC/MS) technique was employed to monitor the evolution of the volatile thermal degradation products exhausted after a growth process of CNTs run at 900 degrees C in Ar atmosphere. The presence of ferrocene catalyst has shown negligible effect on the composition of the volatile products and the main decomposition molecule detected was benzene. Furthermore, the comparison of GC/MS results with scanning electron microscopy images and Raman spectra of the as-grown samples have suggested that the presence of benzene and its interaction with the iron clusters play a key role in the CNT formation, but only on the bare silicon wafer.

Human plasma protein adsorption on carbon-based materials.

In this study the initial reactions of different carbon-based materials with human blood were investigated by short-time exposure to platelet poor plasma (PPP). Extent of protein adsorption and conformational changes of proteins adsorbed on material surfaces are known to be keys factors affecting further biological reactions. Plasma protein adsorption on multi-walled carbon nanotubes (MWCNTs), highly oriented pyrolytic graphite (HOPG) and nanocrystalline graphite (NG) were investigated and the results obtained on these materials were compared with those obtained studying pyrolytic carbon (PyC), a material showing good anti-trombogenic properties. The quantification of adsorbed plasma proteins on sample surfaces was obtained by Micro BCA Protein Assay, while immunofluorescence analysis was employed to monitor the surface density and distribution of two selected proteins, namely fibrinogen (Fg) and Hageman factor (FXII), proteins playing a leading role in mediating platelet adhesion. The dependence of the biological response on the surface chemical and morphological properties were also investigated and data obtained using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are presented. After PPP incubation PyC is characterized by the presence of low level of whole proteins and FXII adsorption, in contrast to a high adhesion of Fg. Compared to PyC the analysis of the other carbon-based materials result in a higher whole protein adsorption with an increasing trend moving from MWCNTs, NG and HOPG respectively. The Fg surface density on PyC, NG and MWCNTs is about four times higher than on HOPG while only HOPG show a detectable fluorescent signal of FXII. If AFM data indicate that surface morphology does not play a crucial role in protein adhesion, XPS analysis show chemical differences that can be correlated with this biological response.