Carbon nanotubes (CNT) are a new form of carbon with exceptional electrical and mechanical properties. This makes them attractive as inclusions in nanocomposite materials with the potential to provide improvements in electrical and mechanical properties and allows for the creation of a new range of multifunctional materials. In this study single wall carbon nanotubes (SWCNT) were dispersed in polystyrene using a solution mixing method, with the aid of a surfactant. A good dispersion was achieved and the resulting nanocomposites were characterized for electrical conductivity and mechanical properties by 3 point flexural and fracture toughness tests. Results show a significant improvement in electrical properties with electrical percolation occurring between 0.1 and 0.2 wt%. A minor improvement was observed in the flexural modulus but the strength and fracture toughness values in the nanocomposites decreased relative to the neat material. Scanning electron microscopy (SEM) was performed to characterize the morphology and fracture surface of the specimens. The results of testing and microscopy show that the presence of the nanotubes has an adverse effect on the crazing mechanism in Polystyrene (PS) resulting in a deterioration of the mechanical properties that depend on this mechanism.

Single-walled carbon nanotubes (SWCNTs) are promising for use in solar cells and photodetectors because of their strong optical absorption in most of the solar spectrum. There have been many reports about the photovoltaic effect in nanoelectronic devices based on individual SWCNTs, but they have been limited by complicated fabrication and miniscule absorption. There has been a growing trend for merging SWCNTs into micro-and macroscopic devices to provide more practical applications. Here we report the photoresponse of macroscopic SWCNT films with a p-n junction at room temperature. Photovoltage (PV) and photocurrent (PC) due to the photothermoelectric (PTE) effect were observed at the junction, and they were larger by one order of magnitude as compared with their values at the metal-SWCNT interfaces. Various factors affecting PV amplitude and response time have been studied, including junction length, substrate, and doping level. The maximal responsivity we observed was 1V/W with samples on Teflon tape, while a fast response time 80 S was observed with samples on AlN substrates. Hence an optimal combination of photoresponse time and amplitude can be found by proper choice of substrate. It was found that PV increased nonlinearly with increase in n-doping concentration, indicating the existence of an optimal doping level. This result also suggests the possibility to further improve photoresponse by changing p-doping level. Finally, we checked the photoresponse in wide wavelength range (360-900 nm), and PV was observed throughout, indicating that the device could potentially be used as a broadband photodetector.

Carbon nanotubes (CNT) are a new form of carbon with exceptional electrical and mechanical properties. This makes them attractive as inclusions in nanocomposite materials with the potential to provide improvements in electrical and mechanical properties and allows for the creation of a new range of multifunctional materials. In this study single wall carbon nanotubes (SWCNT) were dispersed in polystyrene using a solution mixing method, with the aid of a surfactant. A good dispersion was achieved and the resulting nanocomposites were characterized for electrical conductivity and mechanical properties by 3 point flexural and fracture toughness tests. Results show a significant improvement in electrical properties with electrical percolation occurring between 0.1 and 0.2 wt%. A minor improvement was observed in the flexural modulus but the strength and fracture toughness values in the nanocomposites decreased relative to the neat material. Scanning electron microscopy (SEM) was performed to characterize the morphology and fracture surface of the specimens. The results of testing and microscopy show that the presence of the nanotubes has an adverse effect on the crazing mechanism in Polystyrene (PS) resulting in a deterioration of the mechanical properties that depend on this mechanism.

Thesis--Auburn University, 2010. / Abstract. Includes bibliographic references.

Nowadays, cancer treatment and tissue regeneration have attracted large amount of attention. Single Wall Carbon Nanotubes (SWNT) possess large surface area and outstanding optical and electrical performance, making it a promising component in cancer therapy and tissue reengineering systems. In this study, four disease treating systems based on SWNT are developed. They are pH-sensitive poly(ethylene glycol)-doxorubicin(PEG-DOX)@SWNT drug release system, temperature sensitive SWNT hydrogel, SWNT based biocompatible magnetic hydrogel and biocompatible SWNT-gelatin-F127-cysteamine hydrogel for tissue engineering. The successfully synthesized target compounds are characterized by FTIR. The in vitro release of drugs from the drug release systems is evaluated upon changes of pH values and the laser scanning. The effect of cancer treatment systems on specific kind of cells are examined by confocal laser scanning microscopy (CLSM). The results indicate that all of the four systems show great potential in the biomedical applications especially in disease therapy applications.

A wrinkling approach was used to study the mechanics of hybrid nanotube/nanocrystal coatings adhering to soft polymer (PDMS) substrates. We focused on three thicknesses: 10 nm, 30 nm, and 40 nm. The approach we used is the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIFMM) technique, which allows measurement of the SWCNT film mechanics by the buckling wavelength and the film thickness by inducing a compressive stress in the films at different strains; 2%, 4%, 6%, 8%, 10%, and 12%. In this thesis, dip-coating method with colloidal nanocrystals was used to enhance the rigidity of the carbon nanotube films by filling the pores of the nanotube network. Our results show an almost two-fold enhancement in the Young modulus of a thin SWCNT film related to the presence of a thin interpenetrating over-layer of the semiconductor nanocrystal.

Single Wall Carbon Nanotubes (SWCNTs) are often synthesized as bundles and are chemically modified via either covalent or non-covalent approaches to prevent aggregation, improve their dispersability and tune their physical properties for a potential application. The spatial distribution and effect of covalent addends on the electronic properties of SWCNTs was characterized using a Scanning Tunneling Microscope but with limited success. The effect of sample preparation was questioned as it often involves sonicating the SWCNTs in either an organic or an aqueous medium. Sonication of SWCNTs in certain common solvents was found to alter their electronic properties. The solvent molecules are broken down via a radical pathway during sonicating leading to the formation of new species that interact with the SWCNTs and in some cases with the catalytic material present. New species such as iron chlorides and oxygen, which were formed for example in o-dichlorobenzene and water respectively, caused p-type doping. Doping was characterized by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A blue shift in the D* mode along with a shift to lower binding energy in the C1s peak was observed from Raman spectroscopy and XPS respectively. The reactivity of the radicals (formed during sonication) towards the structure of the SWCNTs was also investigated. Radicals formed during sonication of certain chlorinated aromatic solvents lead to the formation of sonochemical polymers, which interacted heavily with the SWCNTs. These interactions, which can be the source of features commonly associated with covalent functionalization, were thwarted by a washing protocol and were found to be non-covalent in nature. The observations are of relevance towards understanding an inadvertent chemical modification during chemical processing, which can impact reproducibility of results that involve wet-chemical processes. However, with such knowledge of the chemistry involved during sample preparation the occurrence of doping can be either circumvented or appropriately used. / Thesis / Doctor of Philosophy (PhD)

Single Wall Carbon Nanotubes (SWNTs), discovered in 1993, have good mechanical, electrical and thermal properties. Polyacrylonitrile (PAN) is an important fiber for textiles as well as a precursor for carbon fibers. PAN has been produced since 1930s. In this study, we have processed SWNT/PAN fibers by dry-jet wet spinning. Purified SWNT, nitric acid treated SWNTs, and benzonitrile functionalized SWNTs have been used. Fiber processing was done in Dimethyl Formamide (DMF) and coagulation was done in DMF/water mixture. The coagulated fibers were drawn (draw ratio of 6) at 95 oC. Structure, orientation, and mechanical properties of these fibers have been studied. The cross-sections for all the fibers are not circular. Incorporation of SWNT in PAN results in improved mechanical properties, tensile modulus increased from 7.9 GPa for control PAN to 13.7 GPa for SWNT/PAN composite fiber, and functionalized SWNTs result in higher improvements with tensile modulus reaching 17.8 GPa for acid treated SWNT/PAN composite fibers. The theoretical analysis suggests that observed moduli of the composite fibers are consistent with the predicted values.

We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the Erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was 1 to 4.5% as the thickness increased from 18 to 265 £gm. We obtained the stable pulse of the mode-locked EDFL (MLEDFL) when the full-width half-maximum (FWHM) decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased from 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps was the thickness of SWCNTs SA increased from 8 to 100 £gm. In EDFL system, we vary group-velocity dispersion (GVD) with different cavity length to achieve optical pulse compression. We got the shortest pulsewidth was 713 fs, and the time-bandwidth product (TBP) was 0.345. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.

The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulse width in passively mode-locked erbium-doped fiber ring laser (MLEDFL) was investigated and measured. The TCP represented the amounts of SWCNTs, which the optical beam encountered when passing through the SWCNTs SA. If the TCP was smaller than 8.25 (£gm x wt%), the spectral bandwidth was below 2 nm. The pulse shaping was dominated by its own self amplitude modulation (SAM) of SWCNTs SA. With further increasing TCP, the soliton-like ML operation was achieved and the spectral bandwidth was expanded to 6 nm. For soliton-like mode locking (ML) operation, the area theorem dominated the pulse shaping. Through area theorem analysis, the estimation of SPM increased as the TCP increased. The adequate enhanced SPM for balancing the slight negative GVD was provided to generate soliton-like ML pulses shorten the pulse width. However, as the TCP increased, the soliton pulse energy decreased. The decreasing soliton pulse energy restricted the further pulse shortening. The results showed that the dependence of the pulse energy and nonlinear self phase modulation (SPM) on TCP enabled to determine the shortest pulse width in MLEDFL based on the area theorem. At optimized TCP of 70.93 (£gm x wt%), it was found that the shortest pulse width of 418 fs. In addition, based on the estimated SPM from area theorem, the nonlinear refractive index n2 was calculated at the level of 0.4 - 1 x 10^-15 m^2/W that was close to the literature values of 10^-15 - 10^-16 m2/W. It provides another way to estimate the nonlinear refractive index except for the Z-scan measurement. We could also estimate the SPM if an active Z-scan measurement was taken to obtain the nonlinear refractive index of the sample. We realized the trend of pulse energy through few samples in MLEDFL, the behavior of pulse width could be theoretically simulated based on area theorem. Hence, with the area theorem analysis, the optimized TCP of SWCNTs SA could be simulated and estimated to generate the shortest pulse width from the trends of pulse energy and estimated SPM. The significant effect of TCP on pulse energy, SPM, pulse width, and spectral bandwidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of key parameters for characterizing the passive MLFL pulse width. Through the study of the dependence of TCP on ML pulses in MLEDFL, it may provide a guideline to fabricate an effective SWCNTs SA to generate the shortest pulse width of the MLEDFL.