Synthesis of vertically aligned CNT arrays using liquid based precursors and their functionalization by conjugated polymers
Author(s)
Advisor
Bengü, ErmanDate
2011Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
152
views
views
42
downloads
downloads
Abstract
In the first part of this work, a new solution based catalyst precursor
application method is developed for growing high quality vertically aligned carbon
nanotubes arrays (VANTA) through alcohol catalyzed chemical vapor deposition
(AC-CVD). For this purpose, various solution based precursor preparation routes are
investigated starting from γ-Al2O3 / Fe(NO3)3.9H2O mixtures and ranging to catalyst
precursors prepared by mixing aqueous aluminium and iron nitrate solutions.
Application of these solutions separately layer by layer on Si(100) substrate resulted
in high quality dense vertically aligned CNT arrays. By varying the metal nitrate
concentration in the precursor solutions, the dependence of the density and quality of
CNT arrays on the catalyst layers are investigated. The CNT array quality and
density are characterized by dynamic contact angle measurements using water
droplets. Higher density CNT arrays resulted in higher contact angle measurements.
The chemical and structural characterizations of CNTs are also done by using TEM,
SEM, EDX and Raman spectroscopy. Some of the samples are found to be super hydrophobic even after 30 minutes of exposure to water. In this effort, application of
subsequent layers of aqueous aluminium nitrate and iron nitrate on oxidized Si(100)
surfaces are found to be most efficient catalyst layer preparation technique resulting
in the highest density of CNT arrays.
In the second part of this work, functionalization of the synthesized CNT
arrays is done for the purpose of achieving good dispersibility of CNTs in aqueous
media. To this end, a new approach is used to ensure stability of the CNT-water
solution. In this approach, conjugated polymer nanoparticles (CPNs) are successfully
used to disperse CNTs through non-covalent functionalization of the sidewalls of
CNTs. The attachment of CPNs to CNTs is characterized by SEM, EDX and TEM.
Moreover, interactions are investigated by UV-VIS, and Raman spectroscopy. The
interaction mechanism of polymer chains with side-walls of CNTs are further
scrutinized by follow-up experiments where two different conjugated polymers with
brominated-alkyl and bare alkyl groups in THF media are mixed with SWCNTs
(commercial), MWCNTs and an-MWCNTs (synthesized in the first part of this
study). The results of this investigation suggested a limited number of docking
configurations of the polymers with the CNT side-walls. Also, it is found that the
defect density of the CNT side-walls play an important role in the nature of the
interaction. Overall, in this work a cheap and effective route for application of catalyst is
developed for the synthesis of dense, super-hydrophobic CNT arrays using ACCVD.
Then, well-dispersion of these CNTs is successfully achieved using CPNs.
Finally, the nature of the interaction between conjugate polymers and CNTs
sidewalls are investigated using experimental techniques.