The production of small diameter (0.7-1.2nm) and high purity single walled carbon nanotubes using a gas-phase catalytic approach has aroused considerable interest in the chemistry of this unique material. Most recently it has been proposed that tubes produced in this manner can be cut by simply grinding them in a soft organic material such as g-cyclodextrin. The results reported on such cutting techniques however concentrated upon microscopy thereby limiting the degree of information, which could be deduced about the type of interaction between the two materials. In this study electronic and vibrational spectroscopy as well as Differential Scanning Calorimetry has been performed upon a ground mixture of the aforementioned single walled carbon nanotubes and γ-Cyclodextrin. The mixture was prepared by grinding in a 30:1 ratio γ-cyclodextrin and single walled carbon nanotubes for approximately two hours with the drop-wise addition of ethanol (1ml) in the first 10 minutes. A similar ground mixture of g-Cyclodextrin and multi walled carbon nanotubes was also prepared to help asses the type and degree of interaction between the single walled carbon nanotubes and the γ-Cyclodextrin. Absorption spectroscopy showed changes to the electronic structure of both the single walled carbon nanotubes and the γ-Cyclodextrin, while evidence from Raman spectroscopy indicates that the cyclodextrins are absorbed via van der Waals forces along the length of the tube inducing a compressive strain. No such evidence for an interaction with multi walled carbon nanotubes was observed suggesting the possibility of a diameter selective interaction. Finally as a comparison a sample containing 5mg of tubes was refluxed in an aqueous solution of γ cyclodextrin (0.3M) for ~72 hour similar to early studies preformed on C60 and γ cyclodextrin
Experimental measurements of nonlinear optical extinction of nanosecond laser pulses by a set of conjugated co-polymer/multi walled carbon nanotube composites dispersed in solution is reported here. The polymer poly(meta-phenylenevinylene-co-2,5-dioctyloxy-para-phenylenevinylene) and multi walled carbon nanotube composites were varied according to nanotube mass content. The fabrication technique employed to produce the composite material is discussed. The experiments were performed using an open aperture Z-scan with 6 ns gaussian pulses at 532 nm from a frequency doubled, Q-switched Nd:Yag laser. The nonlinear optical extinction of the incident pulses displays enhanced dissipation of the incident light for lower incident intensities relative to increasing multi walled carbon nanotube content. Either the multi walled carbon nanotubes or the polymer dominates the nonlinear response of the composite depending on the relative mass of polymer to nanotube. Mechanistic implications of the optical dissipation are also discussed and investigated via angular dependent scattering measurements.
KEYWORDS: Composites, Polymers, Polyurethane, Transmission electron microscopy, Scanning electron microscopy, Artificial muscles, Microscopy, Single walled carbon nanotubes, Crystals, Analytical research
Today, many materials are being investigated as possible artificial muscle devices. Nanotubes and conducting polymers are two of the most attractive materials for this application, because of their low operating voltage. In this research, a number of materials are investigated, including nanotube based polymer composites. Methods of characterisation include thermal analysis using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), hot stage microscopy and polarized light microscopy were used to evaluate the morphology of the composites. Fourier transform infrared spectroscopy was used as a compliment to the DSC and hot stage microscopy to examine the crystallinity. Gel permeation chromatography (GPC) was employed to determine the effect of the nanotubes on the molecular weight of the polymer. Since the application of this research is a biomedical device, the biocompatibility of the composites was examined using contact angle analysis and cytotoxicity tests. In summary, results to date indicate that these materials have promise as possible artificial muscle devices.
In this research study carbon nanotubes were investigated as possible reinforcement agents to improve the mechanical and thermal properties of two different polymer matrix systems. The polymer matrices systems examined were polyvinyl alcohol and poly(9-vinyl cabazole). It was found by adding a range of mass fractions of carbon nanotubes that both Young's modulus and hardness as measured by nano-indentation increased dramatically for both matrices. Thermal properties were examined using differential scanning calorimetry and thermo gravimetric analysis. An increase of 82% in Young's modulus and 63% in hardness was observed for polyvinyl alcohol while adding approximately 1% by weight of multi walled carbon nanotubes. In the case of poly(9-vinyl cabazole) an increase of 200% in Young's modulus and 100% in hardness was achieved, by adding only 8% by weight of nanotubes. As far as the authors are aware this is the highest increase of mechanical properties observed when using carbon nanotube as a reinforcing agent. In addition the thermal properties varied significatly on introduction of the nanotubes. An increase of crystallinity was found for the semi-crystalline matrix, while a second phase appeared for the amorphous polymer when increasing the amount of multiwalled carbon nanotubes. Mechanical and thermal properties of the used polymer matrices could be significantly increased.
We have fabricated two conjugated organic polymer-multiwalled carbon nanotube (MWNT) composites and measured the MWNT content of these two hosts using electron paramagnetic resonance (EPR). These polymers were poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) and poly(9,9-di-n-octylfluorenyl-2,7'-diyl) (PFO). These polymers both disperse MWNTs efficiently but differ in that PFO also suspends graphitic nanoparticles. The fraction of available MWNTs suspended in PmPV rises with increasing polymer mass before saturating at approximately 50% by mass for an optimum soot to polymer mass ratio of 1:4. The optimum settling time for PFO composites was 96 hrs after which 35% of available MWNTs remained suspended. Finally the host polymers were removed by Buchner filtration and the remaining residues were investigated with transmission electron microscopy (TEM). PFO also suspends graphitic nanoparticles with a maximum diameter of approximately 100 nm, which can be attributed to the structure of the polymer itself.
The change in morphology of a polymer matrix upon the introduction of carbon nanotubes is characterized in this study. Multi-walled carbon nanotubes were dispersed in the conjugated copolymer poly(m-phenylenevinylene-co-2,5-dioctyloxy-p-phenylenevinylene) (PmPV) to produce a composite material. Photoluminescence (PL) measurements show a reduction in PL efficiency as the nanotube content is increased. Electron microscopy studies have shown an ordering of the polymer around the nanotubes allowing a layer thickness of 25nm to be estimated. This observed thickness agrees well with the expected value of 55nm calculated using a model relating the PL decrease to the changes in conformation that result from polymer - nanotube interactions. Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) techniques have been employed to investigate how the polycrystallinity of the polymer is affected due to the presence of nanotubes. The results indicate an increase in polymer crystallinity occurs due to an interfacial interaction between the polymer and the nanotube.
Experimental measurements of optical limiting of nanosecond laser pulses by two distinctly different polymer and carbon nanostructure composite materials dispersed in solution is reported here. The polymer poly(para-phenylenevinylene-co-2,5-dioctyloxy-meta-phenylenevinylene) was used to form exclusive multi walled carbon nanotube and polymer composites. The polymer poly(9,9-di-n-octylfluorenyl-2,7-diyl) was used to form composites consisting of multi walled carbon nanotubes, other clearly defined carbon nanoparticles and polymer. The fabrication technique and material characterization steps are described, where it was found that the carbon nanostructures were stably dispersed in the polymer matrix in both cases. A range of each of these composites was prepared and varied according to carbon nanostructure mass content. The optical limiting experiments were performed using an open aperture Z-scan apparatus with 6 ns gaussian pulses at 532 nm from a frequency doubled Q-switched Nd:Yag laser. In the poly(para-phenylenevinylene-co-2,5-dioctyloxy-meta-phenylenevinylene) and exclusive multi walled carbon nanotube composite either the multi walled carbon nanotubes or the polymer dominates the nonlinear response depending on the relative mass of polymer to nanotube. In the other material saturation of the optical limiting was reached at carbon nanostructure mass percentages in excess of 3.8%, relative to the polymer mass, while the polymer exhibited no response of its own. Furthermore, the scattering of high intensity light from the materials was qualitatively probed and its angular dependence investigated. The nature of the carbon nanostructure inclusions in each material was found to significantly influence the scattering response of the composites.
In this work, mechanical properties of hybrid materials fabricated from nanotubes and commercially available polymers were investigated. It was found that, by adding various concentrations of arc discharge multiwall nanotubes, both Young’s modulus and hardness increased by factors of 1.8 and 1.6 at 1wt% in PVA and 2.8 and 2.0 at 8wt% in PVK, in reasonable agreement with the Halpin-Tsai theory. Furthermore, the presence of the nanotubes was found to nucleate crystallization of the PVA. This crystal growth is thought to enhance matrix-nanotube stress transfer. In addition, microscopy studies suggest extremely strong interfacial bonding in the PVA-based composite. This is manifested by the fracture of the polymer rather that the polymer-nanotube interface. The dependence of the polymer nanotube interfacial interaction on host polymer was studied by intercalating various polymers (PVA, PVP and PS) into single wall nanotube buckypaper. Even for short soak times, significant polymer intercalation into existing free volume was observed. Depending on the polymer and the level of intercalation tensile tests on intercalated sheets showed that the Young’s modulus, strength and toughness increased by factors of 3, 9 and 28, respectively. This indicates that the intercalated polymer enhances load transmission between nanotubes due the significant stress transfer. The level of stress transfer was observed to scale with polymer hydrophobicity as expected.
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