Electrically conductive superhydrophobic octadecylamine- functionalized multiwall carbon nanotube films Haiqing Yao a , Chien-Chia Chu b , Hung-Jue Sue a,b, * , Riichi Nishimura c a Materials Science and Engineering Program, Texas A&M University, College Station, TX 77843, United States b Polymer Technology Center, Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, United States c Corporate R&D Division, Kaneka Corporation, Osaka 530-8288, Japan ARTICLE INFO Article history: Received 2 August 2012 Accepted 9 November 2012 Available online 17 November 2012 ABSTRACT Electrically conductive, superhydrophobic multiwall carbon nanotube (MWCNT) thin films were prepared by direct amination of MWCNTs with up to 14 wt.% of octadecylamine (ODA) by vacuum filtration method. The ODA-functionalized MWCNT films exhibit a high water contact angle of 165° and electrical conductivity of 860 S/m. The liquid–air–solid interface is directly observed from above the water droplet using an optical microscope. The obser- vation indicates that the wettability state of the MWCNTs has changed from relatively hydrophilic to superhydrophobic state upon functionalization with ODA. The fundamental mechanisms responsible for the unusual combination of surface superhydrophobicity and high electrical conductivity of the MWCNT films are described and their implications are discussed. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Recently, electrically conductive superhydrophobic carbon nanotube (CNT) films have received considerable attention for use in various applications such as solar cells [1], flexible optical devices [2] and electrical devices [3]. To fabricate superhydrophobic films, the surface roughness and surface energy state of the material must be considered. Surface functionalization or control of CNT film texture can help manipulate their wettability and lead to superhydrophobicity. In early studies, Jiang et al. [4] reported that aligned CNTs showed a high water contact angle (CA) of about 159°. How- ever, water droplets are not stable on the aligned CNT films and eventually penetrate into the gaps within the CNT forest. To overcome this problem, low surface energy polymers are often used to coat the aligned CNTs. Poly(tetrafluoroethylene) coated CNT forests exhibited a remarkable superhydropho- nicity with a CA of 170° [5]. A superhydrophobic surface was also prepared by coating fluoroalkylsilane, and the film showed a CA of about 171° [6]. However, one drawback with polymer coating is the reduction of the film electrical conduc- tivity. Furthermore, the potential application of aligned CNT superhydrophobic materials is limited due to the difficulty in their preparation [5]. Randomly laid CNT films, as opposed to aligned CNT films, would provide a much easier and more economical method to prepare superhydrophobic films. There are two main ap- proaches for producing superhydrophobic CNT films: (1) adsorption or wrapping by low surface energy polymers as a result of van der Waals forces and p–p interactions [7] and (2) covalent attachment of hydrophobic groups through reac- tions on the conjugated skeleton of CNTs [8–10]. The first ap- proach is best demonstrated by Luo et al. [7] who took advantage of the good compatibility between Nafion and CNTs to fabricate Nafion/CNT nanocomposite films by the vacuum filtration process. The CNT composite film attained a CA of 165° and a small sliding angle (SA) of 3.3° with 9.8 wt.% Nafion. Poly(dimethylsiloxane) coated randomly laid 0008-6223/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2012.11.023 * Corresponding author at: Materials Science and Engineering Program, Texas A&M University, College Station, TX 77843, United States. Fax: +1 979 845 3081. E-mail address: hjsue@tamu.edu (H.-J. Sue). CARBON 53 (2013) 366 – 373 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon