| Carbon nanotubes exhibit outstanding mechanical, electrical and thermal properties and thin films fabricated from them possess several advantages including distinguished electrical conductivity, transparency as well as flexibility simultaneously. Thus, these materials showed great merits in the area of flexible electronics, plastic solar cells, organic light-emitting diodes and roll-up displays. This dissertation was design to disperse carbon nanotubes both through chemical modification and non-covalent dispersion. Based on these two dispersion methods, different techniques for the preparation of carbon nanotubes conducting thin films were proposed. Moreover, the doping process of SWNTs thin film via APS aqueous solution was also investigated. The main results and significance are summarized as follows:1. Single-walled carbon nanotubes(SWNTs) and multi-walled carbon nanotubes(MWNTs) were oxidized by a simple wet method involving a treatment in an aqueous ammonium persulfate(APS) solution at a certain temperature. The oxidation of SWNTs was analyzed as a function of the temperature and the APS concentration. Fourier transform infrared spectroscopy(FTIR) and X-ray photoelectron spectroscopy(XPS) demonstrated that large amount of oxygen-containing groups were attached to the oxidized SWNTs under all reaction conditions, which rendered them functionalized and enabled them to have a high solubility in polar solvents such as water and dimethyl formamide(DMF). At high reaction temperature, images of atomic force microscopy(AFM) showed that both long and short SWCNTs could be obtained by varying the APS concentrations. At low reaction temperature, on the other hand, only long functionalized SWCNTs could be obtained. In the case of MWNTs, besides the above-mentioned phenomenon of cutting and functionalization, an exciting result of layer-by-layer etching of the MWNT graphitic cylinders with the increase of reaction time was observed by XPS and high resolution transmission electron microscopy images (HRTEM). The presented wet chemical oxidation technique provided a facile means of preparing soluble shortened carbon nanotubes in large scale. 2. A layer-by-layer (LBL) technique was exploited to fabricate SWNTs composite thin films onto plastic substrate (PET and BOPP substrate). SWNTs were negative charged through APS oxidation. Via the electrostatic attraction and hydrogen bonding between oxidized SWNTs and polycations such as Poly allylamine hydrochloride (PAH) and Poly diallyl dimethyl ammonium chloride (PDDA), homogenous films of SWNTs could be formed. The impact of various factors such as SWNTs concentration, PDDA concentration, solvent on the LBL process and the conductivity of SWNTs thin film were also investigated. UV-vis spectra and sheet resistance were utilized to monitor the LBL process. When the LBL assemblies were realized with a stable0.05mg/ml dispersion of SWNTs oxidized by10%APS treatment at70℃for4h as component no.1and0.5mmol/ml PDDA aqueous solution as component no.2. After20bilayers deposition, the electrical conductivity of SWNTs thin films reached4.57S/cm on PET substrate and2.12S/cm on BOPP substrate.3. A scalable and simple method for the fabrication of SWNTs based optically transparent and electrically conductive thin films was demonstrated in this work. SWNTs coating fluids were prepared by dispersion SWNTs into water with the assistance of worm-like micelle system. The CTAOH/p-toluenesulfonic acid worm-like micelle systems show temperature sensitive and remarkable reheological behaviors. Based on these properties of worm-like micelles, SWNTs thin films could be fabricated through rod coating method. A multistep method was utilized to totally remove the surfactants from SWNTs thin films. The sheet resistance of as prpepared SWNTs thin films at the transmittance of78%is as low as1086Ω/sq. After doping by immersion into thionyl chloride, sheet resistance of SWNTs thin films could further decrease to480Ω/sq. This coating technique shows great merit in both the scalable fabrication of transparent conductive SWNTs thin films and the deposition of various well-defined nanostructures onto plastic substrate.4. SWNTs thin films were doped by immersion into1mol/LAPS aqueous solution. UV-vis-NIR spectra demonstrated that charge transfer doping process was happened between the SWNTs film and APS. The impact of temperature and pH on the doping effect was indicated by the sheet resistance of SWNTs thin films. With the increase of pH or the decrease of temperature, a dramatic increase of conductivity could be obtained. The sheet resistant of SWNTs thin films could decrease approximately2.5times when the films were doped at0℃. At the room temperature, the sheet resistance of SWNTs transparent films could maintain stable for more than72h. However, with the increasing of time, the sheet resistance of SWNTs thin film would increase to that of as prepared thin film at approximately400h. |
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