Bifunctional polyamines for the aqueous dispersion of carbon nanotubes and the formation of carbon nanotube-impregnated
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Bifunctional polyamines for the aqueous dispersion of carbon nanotubes and the formation of carbon nanotube-impregnated hydrogel composites Michael J. Moehlenbrock, Department of Chemistry, Saint Louis University, St. Louis, Missouri 63103 Matthew T. Meredith and Shelley D. Minteer, Department of Chemistry, Saint Louis University, St. Louis, Missouri 63103 Departments of Chemistry and Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 Address all correspondence to Shelley D. Minteer at [email protected] (Received 25 July 2011; accepted 16 August 2011)
Abstract The extraordinary electronic, thermal, and mechanical properties of carbon nanotubes (CNTs) make them attractive materials for incorporation into polymer films. However, retaining these outstanding properties of CNTs during processing can be difficult due to the attractive forces that cause the nanotubes to bundle together. In this study, six different hydrophobically modified linear poly(ethylenimine) (LPEI) polymers are evaluated and effectively used as aqueous nanotube dispersants. This study also shows that the polymers are bifunctional in nature as aqueous polymer/nanotube mixtures can be cross-linked into CNT-impregnated hydrogels.
The effective dispersion/solvation of carbon nanotubes (CNTs) in aqueous solvents is extremely difficult due to the hydrophobic nature of CNTs and the van der Waals forces that exist between individual tubes. These forces cause aggregation of the CNTs,[1–3] which makes it difficult to form polymer composites with evenly dispersed CNTs. Many studies have shown that evenly dispersed CNTs within polymer matrices result in composites with more advanced electronic and/or physical properties.[4–6] In order to achieve more uniform dispersions of CNTs, many different methods have been employed, including covalent[7–9] and non-covalent[7,8,10] modification of the surface of CNTs, the use of a wide variety of surfactants,[11–14] and the use of polymer additives such as poly(vinylpyrrolidone).[15] The covalent modification of CNTs to achieve more effective dispersions is effective, but has drawbacks. Covalent modification of CNTs can result in a loss of aspect ratio and/or conductivity of the tubes, and the use of surfactants in combination with polymers and nanotubes is likely to change the properties of the polymer/CNT composites or add an additional processing step to remove the surfactants. Therefore, it is desirable to design a polymer that acts as a surfactant itself, and can effectively disperse the CNTs before being cast or spun into a film or hydrogel. This type of system has been developed using a few different types of polymers, including a poly(styrene)/poly(acrylic acid) copolymer[16] and hydrophobically modified poly(vinylpyridine).[17] Our group is interested in finding new matrices in which to immobilize enzymes and CNTs together to enhance the performance of enzymatic bioelectrodes. Polyamines are one group of polymers that can be cross-linked in the presence of enzymes to st
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