Self-assembled Multi-walled Carbon Nanotube Coatings
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1057-II20-25
Self-assembled Multi-walled Carbon Nanotube Coatings Kristopher Behler, Mickael Havel, Davide Mattia, and Yury Gogotsi Material Science and Engineering and A. J. Drexel Nanotechnology Institute, Drexel University, 3141 Chestnut Street, Philadelphia, PA, 19104 ABSTRACT Multi-walled carbon nanotube (MWCNTs) grafting onto electrospun poly(acrylonitrile) (PAN) nanofibers and silicon carbide (SiC) microfibers yields a layer by layer deposition of self assembled nanotube filaments or nanowires. PAN fibers were first functionalized with carboxylic groups through a sodium hydroxide treatment. Then, poly(diallyldimethylammonium chloride) (PDDAC), a positively charged polyelectrolyte was adsorbed onto the fibers via electrostatic interaction. When placed in contact with the modified fibers, acid treated MWCNTs (ac-MWCNTs) self-assemble onto the polymer nanofibers. The electrical conductivity of nanofibers improves due to the formation of a continuous MWCNTs monolayer on the surface, as opposed to traditional incorporation of large amounts of nanotubes into the bulk of the polymer. The use of polymers capable of forming hydrogen bonding with ac-MWCNTs, e.g. polyamides, further offers a perfect scenario in which no binding agent (PDDAC) or polymer modification is required. Polyamide 11 (PA 11) has been electrospun to provide a dense network of 100 nm and greater fibers for deposition of ac-MWCNTs. The resulting mats yielded an electrical conductivity of about 0.1 S/cm. INTRODUCTION Much effort has been invested to develop nanotube-containing materials [1-12]. However, since both single-walled (SWCNTs) and multi-walled carbon nanotubes do not disperse easily in solvents and polymer solutions due to their strong tendency to form bundles and aggregates, composite materials loaded with carbon nanotubes often show little or no improvement in their mechanical properties [6,10,12,13] with a modest increase in electrical conductivity, unless either very expensive SWCNTs or large amounts of MWCNTs are used. While many efforts have been dedicated to improving the dispersion of the nanotubes by using surfactants [14-16], polymer wrapping [1] or functionalization of the nanotube’s outer walls [1719], control over the nanotubes’ distribution remains a challenge. Nanotubes have been successfully incorporated into polymer nanofibers [20] but only a limited number of studies on nanotube coating on nano- or micro-fibers has been reported [21]. In this paper, we report a new approach based on the self-assembly of MWCNTs onto electrospun nanofibers and other surfaces. This room temperature process, which was initially demonstrated on flat surfaces[22], is promising given its simplicity and efficiency. Furthermore, monolayer coatings are a cost-effective alternative to the massive incorporation of nanotubes into bulk polymers when achieving a high electrical conductivity is the main reason for adding nanotubes.
EXPERIMENTAL MWCNTs, PA 11 pellets (BESVOA grade) and powders (D30 and D150 grades) were provided by Arkema (France) [23].
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