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Controlling alignment and orientation in carbon nanotube films fabricated using inkjet printing

University of British Columbia

Carbon nanotubes (CNTs) are a fascinating material with a diverse set of electrical and mechanical properties. In particular, they exhibit either metallic or semiconducting behaviour depending on their size and molecular configuration. This ability to tune their electrical properties makes CNTs applicable to a diverse range of electronics applications. One of the long-standing barriers of their application is in the difficulty of controlling their position and orientation on a substrate. This is not only true for applications utilizing individual CNTs, but also for large-scale electronics such as sensors and displays, where CNT thin films are of great interest. The CNTs in such films are typically randomly entangled and do not exhibit the same excellent properties observed in individual CNTs. However, when the CNTs possess long range mutual alignment the electrical properties of the film can be improved. The objective of this research was to design a process for fabricating films of mutually aligned CNTs with a controlled orientation using solely inkjet printing. The innate lyotropic liquid crystallinity of highly concentrated CNT suspensions was used here as a mechanism of achieving long-range mutual alignment. The CNT orientation was found to depend on the evaporation behaviour, which was dictated by the printed pattern. A unique printing scheme was developed in order to achieve the necessary high concentrations for a lyotropic liquid crystalline phase transition, and the morphology of the resulting films was studied using scanning electron microscope (SEM) and polarized light microscopy. It was found that the alignment does not necessarily persist throughout the depth of the film, but is strikingly evident on its surface. In order to both isolate the aligned surface layer and investigate the sub-surface morphology, a method was developed for removing thin consecutive layers from the film using a polydimethylsiloxane (PDMS) stamp. SEM results indicated that the CNT film morphology was one of stacked layers, each exhibiting a decreasing degree of alignment. These results were supported by polarized light microscopy and are suggestive of a smectic liquid crystal structure.

Text

2012-01-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/39938

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/