(Left) X-ray photoelectron spectra of C1s level of MWNT after SEEP functionalization in presence of Acrylic Acid. (Right) TEM images of a single MWNT with grafted PHEMA 15nm thick (insert: zoom of the CNT surface)
Due to their outstanding properties (Young modulus E = 45 GPa, conductivity = 1 GA cm-2), carbon nanotubes (CNTs) have recently subjected lot of attraction. Indeed, CNTs find applications in different topics such mechanical reinforced composite materials, microelectronics, and biology for example. However, CNTs are poorly soluble and prone to aggregation in bundles.
Thus, processing of CNTs is a key point for future applications and requires appropriate chemical modification. Among the numerous methods published in recent literature for functionalizing CNTs, chemical and electrochemical grafting appear the most frequent. In particular, atom transfer radical polymerization (ATRP), covalent anchoring of preformed polymer chains and electrografting of diazonium salts on CNTs have recently been reported.
We first studied cathodic electrografting on CNTs using the Surface Electroinitiated Emulsion Polymerization (SEEP) process, where diazonium salts are used both to initiate the radical polymerization of vinylic monomers in solution and to form a primer grafted polyphenylene like layer on the carbon surface. SEM and TEM analysis revealed that ultrathin polymer films are grafted on carbon nanotubes sidewalls. XPS spectroscopy further confirmed the functionalization of multi-walled carbon nanotubes.
We then investigated purely chemical grafting of polymers onto CNTs, using the GraftFast® technology. That new method proved very efficient to functionnalize CNTs from suspensions, both in organic and aqueous solutions.
In parallel, direct electrografting was compared to competing methods to create grafted polymer chains on surfaces, such as ATRP from grafted diazonium salts.  That latter technique allows a fine control of the thickness of the polymer film, together with a higher versatility when compared to direct cathodic electrografting of vinylic polymers. However, the experiment requires two distinct steps (first electrografting of a specially designed diazonium salt, which acts then as the initiator for the second step; second, ATRP-growing of the polymer) and is quite slow. It is thus more suited when a fine control of the grafted thickness is required.
(1) Gohier, A.; Nekelson, F.; Deniau, G.; Palacin, S.; Mayne L'hermite, M.; Reynaud, C. "Controlled grafting of functional polymer films onto multi-walled carbon nanotubes using diazonium salt based one-pot process." Chem. Mater. (2009) submitted.
(2) Palacin, S.; Charlier, J.; Deniau, G.; Jegou, P.; Jousselme, B.; Mouanda, B.; Viel, P.; Grafting organics on Surfaces: Chemical and Electrochemical Methods. Molecular and Organic Electronic Devices. D. K. Aswal and J. V. Yakhmi, Nova Sciences Publishers. (2009) in press.(ISBN: 978-1-60876-594-2)
(3) Tessier, L.; Chancolon, J.; Alet, P.-J.; Trenggono, A.; Mayne l'Hermite, M.; Deniau, G.; Jégou, P.; Palacin, S.; "Grafting organic polymer films on surfaces of carbon nano-tubes by Surface Electroinitiated Emulsion Polymerization." Physica Status Solidi A 205 (2008) 1412-1418.
(4) Mévellec, V.; Roussel, S.; Tessier, L.; Chancolon, J.; Mayne-L'Hermite, M.; Deniau, G.; Viel, P.; Palacin, S. "Grafting polymers on surfaces: A new powerful and versatile diazonium salt-based one-step process in aqueous media." Chem. Mater. 19 (2007).: 6323-6330.
(5) Vast, L., Rochez, O., Azoulay, L., Fonseca, A., Nagy, J.B., Deniau, G., Palacin, S., Delhalle, J., Mekhalif, Z. "Formation of an adherent polyacrylonitrile/carbon nanotubes composite film onto a polyacrylonitrile brush electrografted on copper." J. Nanoscience Nanotechnology 7(2007) 3404-3410.
(6) Matrab, T., J. Chancolon, Mayne L'Hermite, M., Rouzaud, J. N., Deniau, G., Boudou, J. P., Chehimi, M. M., Delamar, M. "Atom transfer radical polymerization (ATRP) initiated by aryl diazonium salts: a new route for surface modification of multiwalled cabone nanotubes by tethered polymer chains." Colloids and Surfaces A 287 (2006) 217-221.
(7) Defever, T., G. Deniau, Goux-Capes, L., Mayne, M., Palacin, S., Bourgoin, J. P."Cathodic electropolymerisation on the surface of carbon nanotubes ." J. Electroanal. Chem 589 (2005) 46-51.