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Title: Carbon nanotubes as near infrared laser susceptors
Author: Bahrami, Amir
ISNI:       0000 0004 2707 849X
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2011
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The coupling efficiency of carbon nanotubes with near infrared laser radiation at 940nm wavelength was investigated. Nanotubes treated with different post processing methods were irradiated at different laser power intensities as dry samples and suspensions in water or ethanol. The interaction with the laser beam was measured and quantified based on the temperature increase in the samples as well as the amount of energy transmitted through them. Parallel experiments using carbon black revealed better performance of carbon nanotubes in terms of coupling efficiency and heat dissipation to their surroundings. It was found that most of the incident radiation on an individual carbon nanotube is absorbed, resulting in extreme local temperature increases proportional to the laser intensity, which can lead to instant tube oxidation in air. Such high heats are efficiently transferred to the material in immediate contact with the nanotubes, increasing its temperature very rapidly. The most intriguing results were obtained in the presence of water where the observations suggested, disintegration of carbon nanotubes with each laser pulse. It is shown that extremely high local temperatures vaporise the water in the immediate vicinity of a carbon nanotube and result in a water-gas reaction. It is further postulated that such effects can be achieved with laser beams at power intensities near the skin tissue's safe exposure thresholds, and therefore can potentially be used as a method of removing nanotubes from living tissue. This has advantages in providing an exit route for nanotubes whether introduced on purpose for reasons of medicine or therapy, or possibly, as a result of inadvertent exposure. Further studies on laser heating and transmission through different dry samples, highlighted that more crystalline structures such as that of a heat-treated nanotube, are more effective in causing extinction of the laser beam and a reduction in the transmitted beam intensity, however the tubes with more defects or with a length comparable to the radiation wavelength are very effective in converting the absorbed laser energy to heat. This effect is exacerbated when the laser beam is polarised parallel to the long axis of the carbon nanotubes. These heating effects were exploited to create welds in high density polyethylene using through transmission laser welding. The resultant welds showed better than or equal mechanical performance to welds made using industrial absorbers such as carbon black or Clearweld®.
Supervisor: Windle, Alan Sponsor: Royal Commission for the Exhibition of 1851 and the Welding Institute
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Carbon nanotubes ; Welding ; Lasers ; Water-gas ; Infrared ; Cancer therapy ; Transmission ; Absorption