Title:
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Dispersion, adsorption properties and separation of nanoparticles
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Recent years have seen a surge in interest into the properties of new materials, and
their application in electronic devices. This project has used techniques common
for colloidal systems in order to gain insight into these systems. The work has
mainly focussed on single-walled carbon nanotubes (SWCNTs), however silicon
nanowires have also briefly been studied.
Pluronic block copolymers are commonly used to stabilise SWCNTs in water,
most commonly F127. Such dispersions were studied using small-angle neutron
scattering (SANS) experiments performed at a range of solvent contrast systems.
The data were successfully fitted to a relatively simple core-shell cylinder model.
Data fitting was consistent with SWCNTs present in small bundles in dispersion,
with an average radius of 10 A, surrounded by a water-swollen F127 layer of 61 A
thickness, with a water content of 94% in the adsorbed layer. Increasing the
temperature of F127 /SWCNT /D20 systems so that they were above the critical
micellisation temperature (CMT) of the polymer was seen to have only a small
impact on the polymer adsorption, with the adsorbed layer thickness increasing
from ~55 to 65 A, and the adsorbed amount increasing by between 50 and 100%
(from ~ 1 to 1.5 mg m- 2).
Dispersions of SWCNTs in surfactant mixtures of SDS and sodium cholate (SC) are
often used to separate SWCNTs by electronic type. SWCNTs were dispersed with
SDS and studied using small-angle scattering techniques at various contrasts. Data
were fitted to a core-shell cylinder model, and the fits were consistent with small
SWCNT bundles of an average radius of 10 A, surrounded by an adsorbed layer of
thickness 18 A. The adsorbed amount of SDS at the SWCNT surface was calculated
to be 2.5 mg m-2 , however the adsorbed amount at the SDS headgroup/water
interface was calculated to be 0.85 mg m- 2
, a value closer to previously reported
values for the adsorption of SDS on carbon surfaces. Subsequently, SWCNTs
dispersed with SC and mixtures of SDS and SC (1:4 and 3:2 volume ratios of
SDS:SC) were studied with SANS, and the dimensions of the decorated SWCNTs
were not seen to vary greatly between the different surfactants studied.
Finally, the separation of nanoparticles has been investigated. The separation of
SWCNTs based on their electronic properties using aqueous PEG/dextran twophase
polymer systems was studied. Although absorbance spectra suggested that
an electronic separation of SWCNTs had occurred, the process was found to be
highly irreproducible. Additionally, variations in temperature were found to have
little effect on partitioning and no separation by electronic type was seen when
F127-dispersed SWCNTs rather than SC-stabilised SWCNTs were used, suggesting
that, unlike F127, SC adsorbs differently to SWCNTs depending on their electronic
type. Silicon nanowires (SiNWs) have also been briefly studied, and separating
the nanowires by length was attempted using glass bead columns, however no
significant separation by length was achieved.
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