Carbon allotropes have taken central stage of nanotechnology in the last two
decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential
building blocks for nanotechnology. Their superlative electrical, thermal and mechanical
properties make them desirable for a number of technological applications
ranging from lightweight strong materials to electrical wires and support for catalysts.
However, transferring the exceptional single molecule properties into macroscopic objects
has presented major challenges.
This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids
and these solution can processed into macroscopic objects. Chapter 2 reviews
neat CNT fiber literature. Specifically, the two main processing methods —solid–
state and solution spinning — are discussed. CNT aspect ratio and fibers structure
are identified as the main variables affecting fiber properties. Chapter 3 shows that
graphite can be exfoliated into single-layer graphene by spontaneous dissolution in
chlorosulfonic acid. The dissolution is general and can be applied to various forms of
graphite, including graphene nanoribbons. Dilute solutions of graphene can be used
to form transparent conductive films. At high concentration, graphene and graphene
nanoribbons in chlorosulfonic acid forms a liquid crystal and can be spun directly
into continuous fibers. Chapter 4 describes a solution–based method to form a thin
CNT network. This network is an ideal specimen support for electron microscopy.
Imaging nanoparticles with atomic resolution and sample preparation from reactive
fluids demonstrate the unique feature of solution–based CNT support compared to
state–of–the–art TEM supports . Chapter 5 describes CNT liquid crystalline phase.
Specifically, CNT nematic droplets shape and merging dynamics are analyzed. Despite
nanotube liquid crystals having been reported in various CNT systems, a number
of anomalies such as low order parameter and spaghetti–like, nematic droplets
are reported. However, CNTs in chlorosulfonic acid show elongated, bipolar droplets
typical of other rod–like molecules. Moreover, their large aspect ratio allows capturing
the transition from homogeneous to bipolar transition expected from scaling
arguments.The equilibrium shape and merging dynamics demonstrate the liquid nature
of CNT liquid crystals. Chapter 6 describes the CNT/chlorosulfonic acid fiber
spinning. The influence of starting material, spinning dope concentration, spin draw
ratio and coagulation on fiber properties is discussed. The linear scaling of fiber
strength with CNT aspect ratio is demonstrated experimentally, once the best properties
from different batches are compared. Moreover, Successful multi–hole spinning
demonstrates the intrinsic scalability of wet spinning to meet the typical production
output of industrial–scale spinning. Chapter 7 compares acid–spun CNT fibers to
other CNTs fibers as well as existing engineered materials. Acid–spun CNT fibers
combine the typical specific strength of high–strength carbon fibers to the thermal
and electrical conductivity of metals. These properties are obtained because of a
highly aligned, dense structure. The combined strength and electrical conductivity
allow acid-spun fibers to be used as structural as well as conducting wire while
the combined electrical and thermal properties allow for exceptional field emission
properties.
In conclusion, we demonstrate that multifunctional properties of carbon nanotubes
that have fuelled much of the research in the past 20 years, can be attained on a
macroscopic level via rational design of fluid–phase processing.
| Identifer | oai:union.ndltd.org:RICE/oai:scholarship.rice.edu:1911/64655 |
| Date | 06 September 2012 |
| Creators | Behabtu, Natnael |
| Contributors | Pasquali, Matteo |
| Source Sets | Rice University |
| Language | English |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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