An improved method for functionalisation of carbon nanotube spun yarns with aryldiazonium compounds Jackie Y. Cai a, * , Jie Min a,b , Jill McDonnell a , Jeffrey S. Church a , Christopher D. Easton c , William Humphries a , Stuart Lucas a , Andrea L. Woodhead a a CSIRO Materials Science and Engineering, P.O. Box 21, Belmont, Victoria 3216, Australia b College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, China c CSIRO Materials Science and Engineering, Bayview Avenue, Clayton, Victoria 3168, Australia ARTICLE INFO Article history: Received 12 April 2012 Accepted 24 May 2012 Available online 1 June 2012 ABSTRACT We report a method for modifying carbon nanotube (CNT) spun yarns with aryldiazonium salts that involves the pH controlled application of the diazonium salts to CNTs both during and after the yarn formation process. This largely facilitates the chemical accessibility to CNTs within the yarn, potentially enabling a more extensive and uniform modification. The modified CNT yarns were characterised by X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy, and also examined for their mechanical properties. The results demonstrated that a CNT spun yarn was effectively modified by this method without impairing the yarn integrity. The formation of oligomerised polyene struc- tures on the CNT surfaces was observed. This modification resulted in an increase in ten- sile strength and Young’s modulus of the CNTyarn. The functional groups grafted on CNTs also provide opportunities to form crosslinks in the yarn to further improve mechanical properties. Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. 1. Introduction Currently, the strength of pure carbon nanotube (CNT) spun yarn formed by drawing and spinning directly from aligned multi-walled CNT forests is several orders of magnitude lower than that of the individual CNTs in the yarn. Insufficient adhesion and load transfer between CNTs in the yarn due to their chemically inert and very smooth surfaces as well as the inherently porous yarn structure (the presence of sub- micron scale pores) are believed to be responsible [1,2]. Mod- ification of the CNT sidewalls in the yarn may be one viable method of improving the strength utilisation of individual CNTs within the yarns. This would essentially involve altering the intertube interactions. Chemical modification of CNT sidewalls can be achieved by grafting specific chemical groups through chemical reac- tions, such as oxidation, fluorination, diazotisation and sub- sequent derivatization [3–10]. However, the use of such reactions on pure CNTyarns may not be suitable. The severe reaction conditions often required can potentially destroy the integrity of the CNT yarns or weaken the CNTs themselves. Ideally a reaction that can be realised under mild conditions with minimal damage to the CNTs is desirable. Based on these considerations, we have adopted the sidewall modifica- tions of CNTs with aryl diazonium compounds where the grafting reactions can be accomplished under mild treatment conditions. The mechanism for the arylation is based on a free radical chain reaction and has been well discussed in the literature [11–15]. The initiation step can follow two possible paths. The diazonium anhydride formed by the Gomberg–Bachmann reaction (near neutral pH) can decompose into an aryl radical 0008-6223/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.05.055 * Corresponding author: Fax: +61 3 5246 4057. E-mail address: Jackie.cai@csiro.au (J.Y. Cai). CARBON 50 (2012) 4655 – 4662 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon