J. Mater. Sci. Technol., 2010, 26(1), 20-26. Preparation of Large Area Double-walled Carbon Nanotube Macro-films with Self-cleaning Properties Ziping Wu 1) , Qianfeng Xu 1) , Jiannong Wang 2)† and Jie Ma 1) 1) School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2) Shanghai Key Laboratory for Metallic Functional Materials, Key Laboratory for Advanced Civil Engineering Ma- terials (Ministry of Education), School of Materials Science and Engineering, Tongji University, Shanghai 200029, China [Manuscript received June 16, 2009, in revised form September 20, 2009] Double-walled carbon nanotube (DWCNT) macro-films with large areas, excellent flexibility and superhy- drophobicity are reported. The area of the macro-film is larger than 30 cm×15 cm, and this large film can be bended, or folded without any damage, and even can be tailored freely. After a simple modification of perflu- oroalkysilane, the surface of the macro-film shows excellent superhydrophobicity with a water contact angle of 165.7±2 deg. and sliding angle lower than 3 deg., the prepared superhydrophobic films showing excellent antifouling, self-cleaning and water-repellent functions. The topographic roughness and perfluoroalkysilane modification are found to contribute to the observed superhydrophobicity. Considering the outstanding elec- tronic, chemical and mechanical properties of DWCNTs, it is expected that this multifunctional DWCNT macro-film has potential applications in many fields. KEY WORDS: Double-walled carbon nanotubes; Large area film; Self-cleaning; Methanol 1. Introduction Extensive studies have been performed on mi- croscopic carbon nanotubes (CNTs) since the dis- covery of carbon nanotubes [1–5] . Recently, there have been growing interests in macroscopic CNTs, because such CNTs can be directly used in many applications such as solar cells, field-emission, or electroluminescence [6–10] . Some methods have been exploited to prepare CNT macro-films, such as seeded catalyst chemical vapour deposition (CVD) method [11–14] , solution deposition methods [15–17] and others [18,19] . The surface state of a CNT macro-film is of sci- entific and technological interest. For example, if the surface of the film is treated to be superhydrophobic, it can possess some new functions such as antifouling, † Corresponding author. Prof., Ph.D.; Tel: +86 21 65982867; Fax: +86 21 65985385; E-mail: jnwang@tongji.edu.cn (J.N. Wang). self-cleaning and water-repellent properties [11] that are useful for wetting environments. Generally, a surface with a water contact angle (CA) larger than 150 deg. and a dynamic sliding angle (SA) less than 10 deg. can be called superhydrophobic [12,13] . The chemical composition and hierarchical nano/micro- structure of a surface are found to be the two main factors for achieving superhydrophobicity [11–13] . CNT is a kind of one-dimensional nano-materials and has obvious advantages for fabricating the special nano/micro-structure needed by superhydrophobic- ity. The vertically aligned CNT film with a needle-like surface structure has been proved to be very suitable for fabricating superhydrophobic surfaces by seeded catalyst CVD [20–25] . Currently, non-aligned carbon nanotube powders and films have also been fabricated for achieving superhydrophobicity [17, 26–29] . However, the fabrication of a CNT film with a large area, good mechanical stability and superhydrophobicity by ap- plying a simple method is still a technical challenge.