Concentrated Solutions of Highly Conductive Pyrene-Functionalized Carbon Nanotubes Suitable for Printing
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Concentrated Solutions of Highly Conductive Pyrene-Functionalized Carbon Nanotubes Suitable for Printing Christopher William Landorf1, James Lamb1, Wu-Sheng Shih2, Vijaya Kayastha1, John Bledsoe1, Jacqueline Garrison1, Marriana Nelson2 1
Printed Electronics Technology Center, Brewer Science, Inc., Springfield, MO, United States.
2
CNT Research, Brewer Science, Inc., Springfield, MO, United States.
ABSTRACT As produced, raw carbon nanotubes are not soluble in many solvents necessary for printing applications. Standard methods for circumventing this problem involve sidewall functionalization and surfactants. Sidewall functionalization invariably destroys the π-network that gives carbon nanotubes their useful electronic properties, while surfactants deposit an insulating layer onto the carbon nanotube surface that must be washed off to regain the desired properties. Non-covalent functionalization offers the possibility to achieve solubility without destroying the π-network, but published methods have resulted in relatively low concentrations or substandard electronic performance. We have developed a scalable method to non-covalently functionalize long (> 3 μm) carbon nanotubes with simple pyrene derivatives. This method produces highly dispersed solutions with concentrations as high as 2.5 g/l that can be used to produce conductive coatings with sheet resistance as low as 350 Ω/sq with 85% transmittance at 550 nm without post-deposition washing or doping treatments. The functionalized carbon nanotubes can be formulated into solutions that can be printed by ink-jet deposition, Aerosol-Jet® deposition, screen printing, and spray coating for printed electronics fabrication, and the solutions are stable for months without signs of bundling. INTRODUCTION Easily deposited conductive films have been a major goal of carbon nanotube (CNT) research for many years [1-3]. Highly conductive coatings of CNTs are not unusual; however, the nature of the solutions that CNTs are deposited from is often not ideal for large-scale printing. Pristine CNTs will not disperse in water at high enough concentrations to make printing practical, so surfactants are employed. Surfactants are insulating, so they must be washed off after deposition, and washing creates a waste stream that contains CNTs and can destroy the film integrity [4,5]. Alternatively, functionalization can produce highly concentrated dispersions of CNTs, but the resulting films have poor conductivity [6-8]. This conductivity can be enhanced with post-deposition treatments, but these treatments are often harsh and the effects are reversible [9,10]. One method that has been used to circumvent these issues is the use of non-covalent functionalization with polyaromatic compounds [11,12]. Our lab has had some success with previous methods for solubilizing CNTs with polyaromatic hydrocarbons (PAHs), but the resulting solutions were disappointing in both concentration and film conductivity. This paper reports on research to devise a novel method for functionalizing CNTs with solub
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