Dispersion and individualization of SWNT in hydrosoluble polymer solutions
Résumé
Carbon nanotubes are widely used as nanocharges in polymer matrix composites for improving
mechanical or electrical properties. Nanocomposites can be prepared either in the solid or in the
liquid state, and in the latter case by mixing nanotubes with either melted polymers or polymer
solutions. To date, controlled dispersion of CNTs in a solution or a composite remains a
challenge, due to the strong van der Waals binding energies associated with the CNT
aggregates. Dispersion of nanotubes with high yields, as well as high amounts of individual
nanotubes, can be prepared in water with the help of surfactants. However, when using such
suspensions as precursors for nanocomposites, the final materials will contain some surfactants
which will influence their physical properties. On the other hand, dispersing nanotubes directly
in polymer solutions without using surfactants leads to low yields and poor individualization.
In this work, we propose an alternative and simple way to disperse single-walled carbon
nanotubes (SWNT) in aqueous solutions of two hydrosoluble polymers, polyvinyl alcohol (PVA)
and polyvinyl pyrrolidone (PVP). We measure the yield using visible-NIR absorption
spectroscopy, and we probe both the chemical environment of the nanotubes and the
effectiveness of individualization from coupled Raman/Photoluminescence studies. First, we mix
aqueous suspensions of SWNT stabilized with bile salts (BS) with aqueous solutions of PVA,
and we evidence a direct exchange of BS molecules and PVA chains at the surface of SWNT.
By contrast, no exchange is observed with PVP. Second, we show that a simple dialysis
process leads to the preparation of aqueous suspensions of SWNT covered by PVA or PVP
with high yields and an effective individualization of the nanotubes. This simple method opens a
new way for preparing surfactant-free polymer matrix composites with high concentrations of
individual SWNT.
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