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CHEMICAL BONDING OF POLYMER ON CARBON NANOTUBE Chengyu Wei, Kyeongjae Cho, Department of Mechanical Engineering, Stanford University, California; Deepak Srivastava, NASA Ames Research Center, MST27A-1, Moffett Field, California ABSTRACT Recently, carbon nanotubes are considered as nanoscale fibers, which can strengthen polymer composite materials. Nanotube-polymer composite materials can be used for micron scale devices with designed mechanical properties and smart polymer coating to protect materials under extreme physical conditions such as microsatellites. To explore these possibilities it is important to develop a detailed atomic scale understanding of the mechanical coupling between polymer matrix and embedded nanotubes. In this work we study the chemical bonding between polymer molecules and carbon nanotubes (CNTs) using molecular dynamics. Study shows that the bonding between polyethylene and a CNT is energetically favorable. Chemical bonds can be formed at multiple sites, which make the mechanical load transfer from the polymer chain to the tube more favorable. We will discuss about the resulting mechanical coupling between the CNTs and polymer matrix to develop efficient nano-composite materials. INTRODUCTION Because of their unusual mechanical [1,2] and electronic properties [3,4], there are extensive studies on carbon nanotube (CNT) as a nano-fiber to improve the performance of a matrix or to achieve new properties [5-8]. One distinguished property of a CNT is its high strength, coming from the strong sp 2 bonds, which makes CNTs good candidates as reinforcement fibers to matrix. The other advantage of a CNT as a fiber is its large surface area, which is good for chemical bonding or adhesion, an important factor for a good composite. One essential issue in the reinforcement of a fiber composite material is that the embedded fibers must have large enough aspect ratio so that there is enough load transfer through the interfacial shear stress and consequently the full strength of the fiber can be used. For a micrometer long CNT with diameter in nano-meter scale, the aspect ratio can be 1000 or higher, which is much larger than usual common fibers. There are experiments using TEM to investigate CNTs (both multi-walled and single-walled CNTs) as reinforcement fibers in polymer matrix [6,8]. Although people found load transfers exist between CNTs and polymer matrix with cases of showing signs of quite large load transfers in some polymer-CNT composites [9], which suggest possible chemical bonding between CNTs and polymers, it is not clear what is the mechanism of the load transfer. It is thus important to understand the mechanism of load transfers at atomic level to facilitate the development of high performance CNT-polymer composites. MOLECULAR DYNAMICS SIMULATIONS When chemical bonding is present, the interfacial shear energy between a fiber and a matrix is typically in range of 50 to 300J/m 2 [10]. If only Van der Waals interactions are W4.7.1

Table I: MD simulations of chemical bonding of hydrogen atom on