Chemical Vapor Deposition of Carbon Nanostructures and Carbon Nanotubes-Reinforced Composites

The vapor deposition of open-networked carbon nanostructures and carbon nanotubes (CNTs)-reinforced composites have been developed and studied parametrically. Carbon nanostructures, including nano-tubes, nano-foams, nanoparticles, and nano-walls, have been deposited on catalyst-assisted substrates using microwave plasma electron cyclotron resonance-chemical vapor deposition (ECR-CVD) system at temperature as low as 300 "C. Processing parameters determining the morphologies and properties of the nanostructures were identified to optimize the productions. Carbon nanotubes-reinforced polymer composite films were synthesized at low temperature by a two-step process using: ( I ) ECR-CVD system to vapor deposit a nanotube film substrate at 480 OC with gas mixture of methane and hydrogen, and (2) chemical vapor infiltration (CVI) of hydrocarbon (CH) polymers into the nanotube substrate. In this study, parylene and glow-discharge polymerization (GDP) polymers were utilized to infiltrate the nanotube substrate at temperature below 70 "C. A strong interfacial adhesion between the carbon nanotubes and the polymer matrix is a major factor that determines the reinforcement performance of such nanocomposites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies showed that nanotubes embedded within the polymer matrix not only provide a chemically compatible interface with the polymer but also enhance interfacial adhesion by mechanical interlocking or entangling. The feasibility of making carbon nanotubes-reinforced composite depends on the processing parameters, including the effect of polymer vapor infiltration and the volume density of the nanotube substrate. Characterizations of these composite films have been conducted and it was found that vapor-deposited parylene/CNTs composite possessed better interfacial bonding and an infiltration distance -200% greater than the GDPiCNTs one, while using a 39 vol.% nanotube substrate. In addition, analyses via nano-indentation measurement revealed that the effect of nanotubes reinforcement within the composite resulted in 14% increase in elastic modulus.