Summary: | Understanding the dynamics of single-walled carbon nanotubes (SWNTs) in simple
and complex environments is crucial for establishing potential application of nanotube
architectures for materials and biosciences. In this thesis we employ the visualization
and analysis tools to image and quantify and the Brownian bending and
diffusion of SWNTs in different media in order to understand and eventually to tailor
nanotube mobility in confined environments.
We image Brownian bending dynamics of SWNTs in water using Near-infrared
(NIR) fluorescence microscopy. The bending stiffness of each chirality-assigned SWNT
is extracted from the variance of the curvature fluctuations. Relaxation times of the
bending fluctuations are measured from the autocorrelation of SWNT shapes. We
find that the bending stiffness scales as the cube of the nanotube diameter, in agreement
with an elastic continuum model. The measured shape relaxation times are
in excellent agreement with the semiflexible chain model, showing that SWNTs may
truly be considered as the ideal model semiflexible filaments.
The motion of stiff objects in crowded environments has been investigated for more
than three decades in polymer science and biophysics; yet, theory and experiments
have not established whether a minute amount of flexibility affects the mobility of
stiff slender filaments. We image the Brownian motion of SWNTs in a network by
NIR fluorescence microscopy. We show direct evidence of SWNTs reptating in the
network, and confirm that their small flexibility enhances significantly their rotational
diffusion. Our results establish the reptation dynamics of stiff filaments and provide
a framework to tailor SWNTs mobility in confined media.
By varying SWNT surface modifications, we can selectively tune the sensitivity
of the carbon nanotubes to the different physical properties of the porous media for
sensing applications. We introduce a simple procedure for dispersion of SWNTs in
aqueous solutions using triblock copolymer, PS-b-P2VP-b-PEO. This process yields
stable dispersions of individual SWNTs without a need for ultracentrifugation, thus
increasing nanotube yield. We show that the SWNT suspension is stable under a
wide pH range as well as high salinity environments. These stable suspensions can
be used in a wide range of applications in different media where stability is crucial.
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