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Small-Angle Neutron Scattering from Aqueous Dispersions of Single-Walled Carbon Nanotubes with Pluronic F127 and Poly(vinylpyrrolidone)
journal contribution
posted on 2012-07-31, 00:00 authored by Meirav Granite, Aurel Radulescu, Yachin CohenAmphiphilic block copolymers are excellent dispersants
for single-walled
carbon nanotubes (SWCNT) in aqueous environments, where their noncovalent
attachments do not affect the π chemical bonding. In this small-angle
neutron scattering (SANS) study, we investigate whether the coverage
of Pluronic F127 polymers around the CNTs depends on the solution
concentration in the range of 1–6% (w/w). The observations
indicate that at these concentrations the SWCNT surface is fully saturated
at about 14 chains per unit length of 100 Å. Furthermore, we
seek to verify whether the unusual effect observed in a previous study
by contrast variation, interpreted as being due to a dense hydration
layer around the polymer chains, also appears using a homopolymer
(polyvinylpyrrolidone - PVP) that does not contain poly(ethylene oxide)
(PEO) units. The SANS patterns showed again a minimal intensity value
at much higher solvent composition (75% D2O) than the expected
value of 29% D2O. The minimum scattering curve exhibited
a nearly q–1 power law at small
angles, an indication of rodlike entities. A model of a CNT thin bundle
with loosely adsorbed polymer chains around it (core–chains)
was reasonably well fitted to the data. The polymer chains are assumed
to be surrounded by a water layer with a slightly higher density than
bulk water, having partial selectivity for D2O.