고성능 복합소재 제조를 위한 나노카본 재료의 기능화 연구

Abstract

Nanocarbon materials such as graphene or carbon nanotube (CNT), have been attracted great attention due to their excellent mechanical, electrical, and thermal properties. However, they also have a disadvantage that their properties deteriorates in the assembled state because of their strong tendency to self-aggregate via van der Waals interaction. In order to overcome this advantage, there have been a lot of studies that produced composites from nanocarbon materials and adequate matrix materials like polymers, and that fabricated functionalized nanocarbon materials for the improved compatibility with properties. In this paper, preparation and evaluation of novel nanocarbon materials by chemical functionalization of graphene oxide and CNT are investigated to present high performances of them. In the part 2, halogen/nitrogen dual-doped graphenes (X/N-G) with thermally tunable doping levels have been newly synthesized by the thermal reduction of graphite oxide (GO) with stepwise-pyrolyzed ionic liquids for the purpose of improved electrical conductivity. The doping process of halogen and nitrogen atoms into the graphene proceeded via substitutional or covalent bonding through the physisorption or chemisorption of in situ pyrolyzed ionic liquids, and it was further investigated by X-ray photoelectron spectroscopy, theoretical calcuation, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. Moreover, X/N-G showed ~22200 S/m of electrical conductivity and ~1021 cm-3 of charge carrier density, much higher than those of thermally reduced GO. In the part 3, direct-spun carbon nanotube fibers (CNTFs) with molecular covalent bridging have been fabricated by a chemical coupling reaction between iodophenyl moieties in the surface of CNTs in order to improve their mechanical properties. CNTs were chemically functionalized with iodophenyl moieties, followed by stepwise thermal treatment which induced rapid molecular cross-coupling reaction, resulting the elimination of iodine. These molecular-bridged CNTFs showed improved mechanical properties compared to raw CNTFs such as 30% enhanced tensile strength and 70% enhanced tensile modulus, while their electrical conductivities did not decrease. In conclusion, novel methods to improve the properties of nanocarbon materials by chemical functionalization of them have been developed and reported in this paper. It is expected that the investigations in this study will help carbon materials to be understood in more detail, and newly synthesized nanocarbon materials by these methods can be used in the various applications.