| dc.description.abstract | Carbon nanotubes have broken through the barriers of our imagination and are currently
being investigated for various nano-electronic device applications. Successful implementation
in these applications however, often requires strict control of their properties
and orientation. As such, post-synthesis processing must be performed prior to any device
fabrication. These processing techniques often aim to either address the challenges associated
with sorting and alignment individually. A novel method called the alignment relay
technique aims to address both of these issues simultaneously. As the introduction of this
process was merely a proof of concept, focus must be put in place to enhance the performance
and e cacy. In an attempt to improve this technique, we alter the temperature,
liquid crystal, iptycene design as well as means of alignment as attempts to accomplish
this. At the same time, mechanistic details are revealed to gain a better insight of the
nanoscopic dynamics.
Preparation of preliminary materials and apparatuses are initially performed. We rst
build a Polarized Optical Microsope (POM) in order to observe the liquid crystal dynamics.
Despite its frequent use in a research setting, the cost can be upwards of thousands of
dollars. As only qualitative observations are required, we decided to build our own model.
In this section, we provide a blueprint for the construction of an economical POM with a
heating stage and digital connection for facile recording of data, totaling about $150-$200.
We subsequently demonstrate its e ective application in visualizing liquid crystals. After
the microscope is made, various molecules are synthesized to gain the chemical resources
needed for the alignment. In an attempt to circumvent some of the hazards asssociated
with the original synthesis, an alternate route to create iptycene (5) is rst explored.
Despite having success in the initial parts of the synthetic sequence, an inability to replicate
literature conditions causes the nal step to produce only a 2% yield. Thus, we are forced
to abandon this procedure and revert to using the original route to making the molecule. A
smaller iptycene molecule (9) is subsequently made through attaching the anchoring group
directly to one of the intermediates appearing in the synthesis of iptycene (5). Finally,
a separate liquid crystal (11) is synthesized through two nucleophilic additions with 4-
hydroxy-4-biphenylcarboxylic acid. These materials provide us the necessary grounding to
perform experiments with the alignment relay technique.
After the preliminary materials are gathered, the e ects of changing the temperature,
liquid crystal and iptycene on CNT depositions are observed. An increase in temperature
from 25 oC to 70 oC with a nematic liquid crystal (ZLI-1185) do not yield great results as
standard deviations are over 45 o. Attempts at using a more ordered smectic A liquid crystal
mixture do not aid results either. In fact, we obtain no CNT deposition at all with these
iv
attempts. From this, we gather that controlling both the alignment and functionalization
of iptycenes at higher temperatures prove to be a challenging task. As a result of the
unknown parameters of both functionalization and alignment kinetics, higher temperature
experiments are abandoned. Next, iptycene (9) is used to probe the sorting e ects of the
alignment relay technique. As the size of the cavity on this molecule is signi cantly smaller
in comparison to the original iptycene (5) we expect smaller CNT's to be deposited onto
the surface. Unfortunately, alignment of this molecule in liquid crystal media is a potential
issue due to the smaller size. Consequently, no CNT's are spotted on the surface. Valuable
mechanistic insights are obtained from these changes in variables in the alignment relay
technique.
Finally, magnetic elds are explored as a viable method for alignment. From these
experiments, we nd that the performance is positively associated with the magnetic eld
strength. The standard deviation in alignment between a 0.6 T eld and 0.9 T eld are
55 o and 24 o respectively with also a clear Gaussian distribution found in the latter
condition. Trends for selectivity however, are uncon rmed as Raman spectroscopy using
532 nm and 633 nm lasers show con
icting information. The 532 nm laser show the
best selectivity under a 0.9 T eld while the 633 nm laser suggested that the 0.6 T has
the better selectivity. Despite needing further data to establish a pattern between eld
strength selectivity, general patterns remain congruent with previous reports as the same
diameter CNT's (1.44 nm and 1.59 nm) are present on the substrate surface. These positive
results allow the use of magnetic elds to be the basis of future alignment experiments and
processes. Bene ts as a result of this change include limiting exposure of the substrate to
dust, adjustable alignment and reusability. | en |
