Vibration characteristics of single- and double-walled carbon nano- tubes functionalized with amide and amine groups S. Ajori, R. Ansari n , M. Darvizeh Department of Mechanical Engineering, University of Guilan, P.O. Box 3756, Rasht, Iran article info Article history: Received 7 October 2014 Received in revised form 19 December 2014 Accepted 7 January 2015 Available online 8 January 2015 Keywords: Functionalized carbon nanotube Amide and amine groups Vibrations Molecular dynamics simulations abstract Carbon nanotube functionalization for designing devices with atomic precision has been of great im- portance in recent years. This article studies the vibration behavior of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) functionalized with amine and amide groups employing molecular dynamics (MD) simulations. The results demonstrate that the natural frequency of CNTs reduces considerably through attaching functional groups to them. Also, it is demonstrated that the natural frequency of DWCNTs is less sensitive to functional groups in comparison with their constituent inner and outer functionalized tubes. Further, it is indicated that the functionalization performed has its most pronounced effect on SWCNTs with small aspect ratios. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Intensive researches on carbon nanotubes (CNTs) have in- troduced them as key nanomaterials in producing different ultra- fine nanoelectromechanical systems (NEMS) due to their surpris- ing physiochemical properties [1–5]. However, there is a drawback to use CNTs under some specific conditions. Because of the poor chemical compatibility and solubility of CNTs with many biological and mineral solvents and also strong van der Waals (vdW) inter- action between their walls, they tend to form bundles. Apparently, the aforementioned properties of CNTs considerably restrict their applications. In order to incorporate CNTs into complex assem- blies, the solubility and compatibility of CNTs should be enhanced through breaking the bundles. The most common and effective way to overcome this drawback is chemical functionalization [6– 10]. As it is proven by experimental evidences [11,12], by in- troducing functional groups to CNTs, not only the desired solubi- lity in different types of media is gained, but also the suitable platform for further functionalization with various organic, in- organic, biochemical and polymeric nanostructures can be pre- pared [13–18]. Additionally, the chemical functionalization can significantly improve the load transfer issues in nanocomposite and through altering the sp 2 hybridization of CNTs to sp 3 , it offers many biotechnological and biomedical applications [19–21]. Amide and amine groups are important functional groups with widespread applications in nanocomposites, sensors and medicine owing to their high reactivity and interesting chemical properties. For example, considering metal-matrix composites, amino-func- tionalized CNTs are used to achieve the improved interfacial Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B Fig. 1. Schematic of functional groups; I. large amide, II. small amide, III. large amine and IV. small amine, gray indicates carbon atom, red and blue express oxygen and nitrogen atoms, respectively, and white atom reveals hydrogen atom. (For interpretation of the references to color in this figure the reader is referred to the web version of this article.) http://dx.doi.org/10.1016/j.physb.2015.01.003 0921-4526/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Fax: þ98 131 6690276. E-mail address: r_ansari@guilan.ac.ir (R. Ansari). Physica B 462 (2015) 8–14