Surface Engineering of Single-Walled Carbon Nanotubes for Electronic and Sensor Applications

Alternative Title
Najeeb C.K.
Najeeb C.K
Alternative Author(s)
Najeeb C.K.
Jae-Ho Kim
일반대학원 분자과학기술학과
The Graduate School, Ajou University
Publication Year
Alternative Abstract
1. The SWNTs are insoluble in most solvents and in polymer solutions in their pristine form, due to the strong van der Waals interaction between nanotube bundles. Among various methods reported in the literature, to impart solubility, i.e. by either physical or chemical modification of SWNTs, non-covalent functionalization of carbon nanotubes is of particular interest, because it preserves sp2 nanotube structure and hence enables one to tailor their intrinsic properties. The objective of our research is to produce stable and conductive solutions of SWNTs and SWNT-polymer for diverse applications including stable and printable ink to use for inkjet printing, fabrication of conductive transparent thin films of SWNTs and SWNT-polymer nanocomposites and their application as transparent electrode in photovoltaic devices, and biocompatibility and sensor applications. 2. Debundling and individual dispersion of single-walled carbon nanotubes (SWNTs) has been demonstrated using a neutral pH water soluble chitosan derivative, N-acetylated chitosan (NACHI), which is synthesized by controlled N-acetylation of chitosan using acetic anhydride. The dispersion of nearly individualized SWNTs achieved by surface modification of nanotubes with a biocompatible polymer can be utilized for electronic and biomedical applications such as field effect transistor, biosensor, scaffold for cell culture and SWNT-biomacromolecule hybrid materials. In order to demonstrate biocompatibility, two types of water soluble chitosan derivatives such as N-acetylated chitosan and chitosan hydroxyphenyl acetamide to disperse SWNTs in neutral pH water, and the biocompatibility of chitosan modified SWNT films was evaluated by culturing HEK-293 cells (Human Embryonic Kidney cell) as a model. The results showed that the SWNT films are highly biocompatible and can serve as good platform for cell adhesion. 3. Nanocomposite inks of poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) filled with SWNTs purified by acidic treatment, carboxylated by chemical oxidation and carboxyl functionalized nanotubes physically modified with a natural gum, gum arabic were prepared. Inkjet printed line patterns of carboxyl functionalized SWNTs based composite demonstrated significant decrease (4 fold) of electrical resistance for the line patterns compared to that with purified CNT based composite due to improved dispersability of nanotubes in the polymer matrix. The use of gum arabic for the dispersion of carboxyl functionalized nanotubes demonstrated a further drastic decrease (18 fold) of the resistance compared with purified CNT based composite owing to the formation of extended continuous network within the line pattern. In addition, we present inkjet printing of aqueous SWNT dispersion stabilized using an anionic surfactant, sodium dodecylbenzene sulfonate (SDBS) and polymer-SWNT complex inks prepared by mixing with aqueous solution of conductive polymers such as polyaniline (PANI), Polypyrrol (PPy) and PEDOT-PSS. The inkjet printed conductive patterns can be applied in various fields, such as flexible high speed transistors, high efficiency solar cells, and transparent electrodes. Furthermore, SWNT/PEDOT?CPSS thin film based device demonstrated high photoconductivity change and enhanced heat transport under UV illumination when compared with device based on SWNT or polymer alone. This property of composite film might open up optoelectronic applications involving photoconductivity, such as photo sensors, organic light emitting diodes (OLED) and organic solar cells. Here in, we demonstrate the application of the SWNT/PEDOT-PSS composite film based device as a UV sensor. 4. We demonstrate a novel, simple and scalable method for the fabrication of aligned ultra-thin transparent conductive films of single-walled carbon nanotubes (SWNTs). Pressing and sliding a thin liquid film of surfactant-stabilized SWNTs or SWNT/polymer complex ink between two parallel flat glass substrates provided high order directional alignment of nanotubes in the plane of the substrate along the sliding direction. The films showed high optical transmittances in the range of 95-98% at 550 nm and corresponding electrical resistances of 700-800 ┯/∋. We also demonstrate the fabrication of well-aligned array of surface modified SWNTs and nano silver decorated SWNTs from their surfactant stabilized dispersions by self-assembly on solid substrates in a large area. The shape, rigidity and surface charge of the nanomaterials are found to be the key factors determining the alignment by self-assembly. The directionally oriented nanotube thin films can be used for applications such as chemical-gas sensor, bio sensors, catalysts, flexible displays, touch screens and solar cells. 5. Transparent conductive thin films of single-walled carbon nanotubes (SWNTs) and their nanocomposites with an organic conductive polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) with different CNT loadings ranging from 20 to 90 wt% were prepared and doped by exposing them to thionyl chloride (SOCl2) vapors. After exposure to SOCl2 vapor for 1h, the SWNT film showed about 15-18 % increase of electrical conductivity, while on the other hand pristine polymer film showed a decrease of electrical conductivity. The SWNT-polymer composite films showed a drastic increase in conductivity by doping with SOCl2 vapor, most interestingly, the doping effect was much higher for composite films with less CNT weight fraction and it was linearly decreased with increasing CNT loading. For instance, composite film with 10 % and 90 % CNT loading demonstrated about 65 % and 10 % increase of electrical conductivity, respectively. The interaction of SOCl2 vapors on SWNTs and composite films is investigated by UV-visible absorption and Raman spectroscopy.

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Graduate School of Ajou University > Department of Molecular Science and Technology > 3. Theses(Master)
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