Biomedical Engineering Reference
In-Depth Information
homogeneously disperse CNTs throughout polymer matrices, the CNT
entanglements and bundles, stabilized by intermolecular van der Waals
forces, must be disrupted. One of the most reported techniques to overcome
these drawbacks is the surface modification of CNTs. In this context,
solvent-based covalent functionalizations are well reported in the literature.
Nevertheless, this type of functionalization presents different drawbacks,
such as CNT insolubility, which can limit control over the grafting of the
functional group onto the CNT surface.
Plasma processes constitute a promising alternative for surface modifica-
tion. Plasma treatments have the advantage of being non-polluting and
provide a wide range of different functional groups depending on plasma
parameters such as power, type of gas used, treatment duration and gas
pressure.
Generally, CNTs are placed inside the plasma, where their surface
interacts with plasma-excited species such as radicals, electrons, ions and
UV radiation which induces the breaking of C-C bonds and the creation of
active sites for bonding of functional groups on the CNT surface.
Argon and hydrogen plasmas are reported to etch CNT surface and end-
caps, improving their field emission properties. When organic monomers are
introduced in the plasma, CNTs are coated with plasma polymer films. This
results in the pre-disaggregation of CNT bundles, which can be well
dispersed in polymer matrices. Fluorinated, oxygenated and nitrogenated
gases were also used to generate functional groups at the CNT surface. This
surface modification of CNTs opens the way for compatibilization with
polymer matrices or for further attachment of other molecules in order to
form polymer nanohybrids. Nevertheless, total control over the grafting of
functional groups on the CNT surface is difficult to achieve when CNTs are
treated directly in the plasma discharge chamber.
To prevent the degradation of the CNTs during plasma treatment, it was
proposed to use plasma discharges as a source of reactive species, such as
radicals, which can interact with the CNT surface outside the plasma
discharge, avoiding structural damage and destruction due to high energy
species bombardment. This process can be considered as a 'dry' chemical
reaction at the CNT surface. The grafted functional groups can be used as
initiator sites for polymerization, yielding CNT nanohybrids that can be
introduced into polymer matrices,
forming high-performance polymer
nanocomposites and nanohybrids.
14.5 References
Ahn K. S., Kim J. S., Kim C. O. and Hong J. P. (2003) 'Non-reactive RF treatment
of multiwall carbon nanotube with inert argon plasma for enhanced field
emission', Carbon, 41, 2481-2485.
