Browsing by Author "Chen, Zheyi"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Cutting of single-walled carbon nanotubes (SWNT): (1) Cutting of pristine SWNT by ozonolysis; (2) Ozonolysis of functionalized SWNT; (3) Cutting ozonated SWNT by e-irradiation; (4) Cutting fluorinated SWNT by pyrolysis
    (2006) Chen, Zheyi; Hauge, Robert H.; Smalley, Richard E.
    Using perfluoropolyether as the solvent, cutting of pristine SWNT has been achieved by extensive ozonolysis with 80% carbon yield at room temperature. The intense disorder mode in the Raman spectra of ozonated SWNT indicates that extensive reaction with the sidewalls of SWNT occurs during ozonolysis. AFM provided a measure of the extent of the cutting effects. Monitoring of the evolved gases indicates CO2 was produced during the ozonolysis process with a dependence on both system pressure and temperature. During heating, FTIR analysis of gases released indicates carbon oxygen groups on the sidewalls of SWNT are released as CO2. Room temperature ozonolysis of fluorinated SWNT and phenol-sulfonated SWNT have also been studied in PFPE. For fluorinated SWNT, etching at the end caps has been demonstrated to be the dominating effect during this process. The improved suspension in 96% sulfuric acid after ozonolysis enables the cutting by ammonia peroxydisulfate without defluorination with a hydrazine treatment. PS-SWNT was found to be effectively cut by ozonolysis in a water suspension with preserved water solubility. Controlled by the electron dosage, a high energy electron beam (3MeV) has been demonstrated to cut ozonated SWNT. Besides ozonolysis, 700°C has been shown an optimal temperature to cut F-SWNT by pyrolysis in an argon atmosphere.
  • Thumbnail Image
    Item
    Single-Walled Carbon Nanotubes (SWNT) polymer composites & composite fibers
    (2008) Chen, Zheyi; Tour, James M.
    With their potentially extraordinary mechanical, thermal, and electrical properties, Single-Walled Carbon Nanotubes (SWNT)/polymer composites and composite fibers may be the ultimate building blocks for next generation ultra-light-weight, ultra-high performance structural applications. However, the dispersity and processibility of SWNT in polymer matrices have been a challenge because of the strong van der Waal attraction between individual nanotubes and their chemical inertness. Predicated on oleum's (100% H2SO 4 with excess SO3) ability to intercalate between individual SWNT inside SWNT ropes, two types of reinforcing SWNT with much improved solubility and dispersity in common solvents were developed: supra-roped SWNT (SWNT-R) and soluble, ultra-short (length<60 nm), carboxylated SWNT(US-SWNT). SWNT-R hold much improved dispersity in super acid and other solvents, and can facilitate the processing of SWNT/polylmer composites and composites fibers. US-SWNT exhibit up to 2 wt% solubility in common solvents. The availability of SWNT-R and US-SWNT open the opportunities for forming high performance composites, blends, and copolymers without inhibiting their processibility. Studies on the synthesis, processing, properties, and morphology of SWNT-R or US-SWNT/polymer composites and composite fibers have demonstrated the reinforcement efficacy of these SWNT in typical thermoset, thermoplastic and liquid crystalline polymer matrices. The epoxy composite system reinforced with 0.5--1 wt% of US-SWNT has shown an average 15% increase in tensile modulus and 50% increase in tensile toughness over those of the neat epoxy. A linear rule-of-mixture calculation indicates the high reinforcement efficiency of US-SWNT in epoxy matrix. The calculated SWNT's elastic modulus approaches the theoretical value. This processible and high performance US-SWNT/Epoxy resin may serve as a matrix material for advanced fiber composites. A novel solution-processing method was introduced to achieve good dispersion of SWNT-R or US-SWNT in Nylon (6, 6) matrix. In comparison to neat resin, increase in tensile modulus and glass transition temperature were observed with 5 wt% nanotubes incorporation. However, the tensile toughness was significant decreased. An advanced SWNT-R/US-SWNT poly(p-phenylene terephthalamide(PPTA) composite fiber system was developed to realize the ultimate SWNT properties and make them processible by conventional fiber spinning processes.