DOI: 10.1002/chem.200700211 Spontaneous Coating of Carbon Nanotubes with an Ultrathin Polypyrrole Layer Martin Pumera,* [a] Br ˇetislav S ˇ míd, [b] Xinsheng Peng, [a] Dmitri Golberg, [c] Jie Tang, [d] and Izumi Ichinose [e] Introduction Composite materials of carbon nanotubes (CNTs) and poly- mers have attracted great interest because they are expected to create advanced functional materials with superior char- acteristics than either of the individual components. [1, 2] CNTs were used to improve the conductivity of polymers, to increase their toughness or to control their bioaffinity. [3] CNTs coated with a precisely controlled polymer layer were fabricated for use as insulated AFM tips, [4] as nanoelectro- des, [5] and as nanowires in nanoelectronic devices. [6, 7] It is particularly interesting to coupling the properties of CNTs with functional polymers, such as polypyrrole (PPy), polyaniline, and polythiophene. [1] It is well known that PPy exists in two oxidation states, one that is doped (oxidized), which has good electrical conductivity, and one that is un- doped (reduced), which has very low electrical conductivi- ty. [8] Coating CNTs with PPy by using chemical and electro- chemical methods have been investigated by several groups, however, the formation of a uniform coating on individual CNTs has remained a challenge because it is not easy to control the agglomeration of conjugated polymers and the polymer chains are prone to forming deposits of irregular nanoparticles or sediments. CNTs have often been embed- ded in bulk PPy, [9] or they were coated with thick and non- uniform layers, which range from 50 [10–13] to 80 nm, [14–16] and often encapsulated more than one CNT in the bulk poly- mer, [11] or they were covered by PPy nanoparticles with a di- ameter of about 50 nm. [12, 13] We previously developed the polymerization-induced ad- sorption process for the preparation of ultrathin films of in- soluble polymers on solid substrates [17, 18] and for nanocoat- ing natural cellulose fibers. [19] Herein we describe the prepa- ration and characterization of nanocoated individual multi- wall carbon nanotubes (MWCNTs) with an unprecedentedly Abstract: A novel protocol for precise- ly coating individual multiwall carbon nanotubes (MWCNTs) with an ultra- thin layer of polypyrrole was devel- oped. The nanocoated MWCNTs were successfully prepared by in situ chemi- cal deposition of polypyrrole in an aqueous suspension of MWCNTs. The coating layer was very uniform and the thickness of the layer was determined by controlling the monomer concentra- tion used, which gave nanometer preci- sion. The products were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, electron energy loss spec- troscopy, and conductivity and current– voltage measurements. The ultrathin polypyrrole layer could electrically in- sulate individual MWCNTs. Keywords: coating · materials science · nanotubes · polymers · polypyrrole [a] Dr. M. Pumera, Dr. X.-S. Peng ICYS, National Institute for Materials Science 1-1 Namiki, Tsukuba Ibaraki (Japan) Fax: (+ 81) 29-860-4706 E-mail: Pumera.Martin@nims.go.jp [b] B. S ˇ míd Department of Surface and Plasma Science Faculty of Mathematics and Physics, Charles University V Holes ˇovic ˇkµch 2, Prague 8 (Czech Republic) [c] Dr. D. Golberg Nanotubes Group, Nanoscale Materials Center National Institute for Materials Science 1-1 Namiki, Tsukuba, Ibaraki (Japan) [d] Dr. J. Tang 1D Nanomaterials Group Innovative Materials Engineering Laboratory National Institute for Materials Science Sengen, Tsukuba, Ibaraki (Japan) [e] Dr. I. Ichinose Functional Thin Films Group, Organic Nanomaterials Center, National Institute for Materials Science 1-1 Namiki, Tsukuba, Ibaraki (Japan) Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author. # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim Chem. Eur. J. 2007, 13, 7644 – 7649 7644