Development of Solution Processable Carbon Nanomaterials and Its Application to Composite and Thin-Film Transistor

Abstract

The solution processable carbon-based nanomaterials, in particular carbon nanotube (CNT) and graphene, were synthesized and functionalized for efficient and easy application. First, a new compatibilizer, poly(vinyl benzyloxy ethyl naphthalene)-g-poly(methyl methacrylate), for poly(styrene-co-acrylonirile) (SAN)/multi-walled carbon nanotubes (MWCNTs) composites was synthesized. It has been identified that naphthalene unit in backbone of compatibilizer interacts with MWCNTs via - interaction and that the graft chain of the compatibilizer is miscible with the SAN matrix. When a small amount of compatibilizer was added to SAN/MWCNT composites, MWCNTs were more homogeneously dispersed in SAN matrix than the case without compatibilizer, indicating that the compatibilizer improves the compatibility between SAN and MWCNTs. As a consequence, mechanical and electrical properties of the composites with compatibilizer were largely improved as compared with those of composites without compatibilizer. Second, A new compatibilizer, poly(vinyl benzyloxy methyl naphthalene)-g-poly(t-butyl methacrylate-co-methacrylic acid), was synthesized for Nylon 66 (N66)/ MWCNT composites. It has been shown that the carboxylic acid unit in the graft chain of the compatibilizer interacts with the amide group of N66. The use of the compatibilizer produces well-dispersed MWCNTs in N66 matrix, which results in improved mechanical and electrical properties of the composites, while the simple mixture of N66/MWNCTs without the compatibilizer exhibits poor mechanical and electrical properties due to severe aggregation of MWCNTs. It is also found that the compatibilizer with a small amount of carboxylic acids is more effective for improving the mechanical and electrical properties of N66/MWCNT composites. Third, novel precursor polymers containing phenylene, naphthalene and anthracene units were synthesized for fabrication of graphene nanoribbons (GNRs) by the Suzuki coupling reaction between dibrominated monomers and diboronic ester monomers. The precursor polymers were converted into GNRs by intramolecular cyclodehydrogenation. The degree of cyclodehydrogenation was determined by analysis of nuclear magnetic resonance spectra. All GNR films show ambipolar charge transport behavior in thin-film transistor (TFT). The GNR film prepared from anthracene-based polymer exhibits the highest TFT performance due to its longer conjugation length and larger width of nanoribbon than GNRs prepared from phenylene and naphthalene-based polymers. Fourth, novel nitrogen-doped graphene nanoribbons (GNR-Ns) were synthesized by the coupling reaction between pyrazine (or benzene) derivative and naphthalene followed by cyclodehydrogenation. The amount of nitrogen doping in GNR-N was controlled by changing the monomer feed ratio of pyrazine to benzene for polymerization. The electron mobility of GNR-N increases while the hole mobility decreases, as the amount of nitrogen doping in GNR increases, indicating that the charge transport behavior of GNRs is changed from ambipolar to n-type semiconductor. The threshold voltage of GNR-Ns also shifts from 20 V to 6 V as the amount of nitrogen doping increases. Finally, the water-soluble conducting polymer, polystyrenesulfonic acid-g-polyaniline (PSSA-g-PANI), easily exfoliates graphenes from graphite and produces well-dispersed graphene in water, which results in improved capacitance of PSSA-g-PANI/graphene composites. It is also found that the longer length of PANI is more effective for improving the capacitance of PSSA-g-PANI composites.