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.
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.
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.
A new route for nanotube-based applications in molecular electronics was developed. Individual polymer strands were assembled onto single-walled carbon nanotubes (SWNT) and multi-walled carbon nanotubes (MWNT) by mechanical agitation. The SWNT hybrid systems have been characterized by electron microscopy (TEM, STM), optical absorption and Raman spectroscopy and a fully nondestructive technique, using electron paramagnetic resonance (EPR), has been developed to estimate the purity of MWNT soot and hybrids. It is demonstrated that solutions of the polymer are capable of suspending nanotubes indefinitely while the majority of the accompanying amorphous graphite precipitates out of solution. Electron microscopy and Raman scattering indicate that through an intercalation process, the ropes of SWNT are destroyed, resulting in individual nanotubes being well dispersed within the polymer matrix. Moreover, Raman and absorption studies suggest that the polymer interacts preferentially with nanotubes of specific diameters or a range of diameters. STM studies showed that the chiral angle of the underlying nanotube is reflected in the polymer coating, demonstrating that the lattice structure of the SWNT templates the ordering in the coating. This could lead to design of specific polymer architectures for selection of desired chiral angles, and hence specific electronic properties.
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