COMPOSITES SCIENCE AND TECHNOLOGY ELSEⅤIER Composites Science and Technology 61(2001)1899-1912 www.elsevier.com/locate/compscitech Advances in the science and technology of carbon nanotubes and their composites: a review Erik t. Thostensona, Zhifeng Ren, Tsu-Wei Chou* Department of Mechanical Engineering and Center for Composite Materials, University of Delaware, Newark, DE 19716, US.A Department of Physics, Boston College, Chestnut Hill, M. 02167, USA Received I May 2001; received in revised form 19 June 2001; accepted 21 June 2001 Abstract Since their first observation nearly a decade ago by lijima (lijima S. Helical microtubules of graphitic carbon Nature. 1991 354: 56-8), carbon nanotubes have been the focus of considerable research. Numerous investigators have since reported remarkable physical and mechanical properties for this new form of carbon. From unique electronic properties and a thermal conductivity higher than diamond to mechanical properties where the stiffness, strength and resilience exceeds any current material, carbon nanotubes offer tremendous opportunities for the development of fundamentally new material systems. In particular, the excep- tional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiff- ness and strength represent tremendous opportunity for application in the 21st century. This paper provides a concise review of recent advances in carbon nanotubes and their composites. We examine the research work reported in the literature on the structure d processing of carbon nanotubes, as well as characterization and property modeling of carbon nanotubes and their composites C 2001 Elsevier Science Ltd. All rights reserved 1. Introduction consequence of their symmetric structure. Many researchers have reported mechanical properties of car- In the mid 1980s, Smalley and co-workers at Rice bon nanotubes that exceed those of any previously niversity developed the chemistry of fullerenes [2]. existing materials. Although there are varying reports in Fullerenes are geometric cage-like structures of carbon the literature on the exact properties of carbon nano- atoms that are composed of hexagonal and pentagonal tubes, theoretical and experimental results have shown faces. The first closed, convex structure formed was extremely high elastic modulus, greater than I TPa(the the C6o molecule. Named after the architect known for elastic modulus of diamond is 1.2 TPa)and reported designing geodesic domes, R. Buckminster Fuller, strengths 10-100 times higher than the strongest steel buckminsterfullerene closed cage of 60 carbon at a fraction of the weight. Indeed, if the reported atoms where each side of a pentagon is the adjacent side mechanical properties are accurate, carbon nanotubes of a hexagon similar to a soccer ball( the Coo molecule is may result in an entire new class of advanced materials often referred to as a bucky ball)[]. A few years later, To unlock the potential of carbon nanotubes for appli- their discovery led to the synthesis of carbon nanotubes. cation in polymer nanocomposites, one must fully Nanotubes are long, slender fullerenes where the walls understand the elastic and fracture properties of carbon of the tubes are hexagonal carbon (graphite structure) nanotubes as well as the interactions at the nanotube and often capped at each end matrix interface. Although this requirement is no dif- These cage-like forms of carbon have been shown ferent from that for conventional fiber-reinforced com- to exhibit exceptional material properties that are a posites [3], the scale of the reinforcement phase diameter has changed from micrometers(e.g. glass and carbon 4 Corresponding author. Tel: +1-302-831-2421; fax: +1-302-831 fibers)to nanometers In addition to the exceptional mechanical properties E-mail address: chou(@ me. udeledu(T.w. Chou) associated with carbon nanotubes, they also posses 0266-3538/01/ S.see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(01)00094-XAdvances in the science and technology of carbon nanotubes and their composites: a review Erik T. Thostensona , Zhifeng Renb, Tsu-Wei Choua,* a Department of Mechanical Engineering and Center for Composite Materials, University of Delaware, Newark, DE 19716, USA bDepartment of Physics, Boston College, Chestnut Hill, MA 02167, USA Received 1 May 2001; received in revised form 19 June 2001; accepted 21 June 2001 Abstract Since their first observation nearly a decade ago by Iijima (Iijima S. Helical microtubules of graphitic carbon Nature. 1991; 354:56–8), carbon nanotubes have been the focus of considerable research. Numerous investigators have since reported remarkable physical and mechanical properties for this new form of carbon. From unique electronic properties and a thermal conductivity higher than diamond to mechanical properties where the stiffness, strength and resilience exceeds any current material, carbon nanotubes offer tremendous opportunities for the development of fundamentally new material systems. In particular, the excep￾tional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube￾reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiff- ness and strength represent tremendous opportunity for application in the 21st century. This paper provides a concise review of recent advances in carbon nanotubes and their composites. We examine the research work reported in the literature on the structure and processing of carbon nanotubes, as well as characterization and property modeling of carbon nanotubes and their composites. # 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction In the mid 1980s, Smalley and co-workers at Rice University developed the chemistry of fullerenes [2]. Fullerenes are geometric cage-like structures of carbon atoms that are composed of hexagonal and pentagonal faces. The first closed, convex structure formed was the C60 molecule. Named after the architect known for designing geodesic domes, R. Buckminster Fuller, buckminsterfullerene is a closed cage of 60 carbon atoms where each side of a pentagon is the adjacent side of a hexagon similar to a soccer ball (the C60 molecule is often referred to as a bucky ball) [2]. A few years later, their discovery led to the synthesis of carbon nanotubes. Nanotubes are long, slender fullerenes where the walls of the tubes are hexagonal carbon (graphite structure) and often capped at each end. These cage-like forms of carbon have been shown to exhibit exceptional material properties that are a consequence of their symmetric structure. Many researchers have reported mechanical properties of car￾bon nanotubes that exceed those of any previously existing materials. Although there are varying reports in the literature on the exact properties of carbon nano￾tubes, theoretical and experimental results have shown extremely high elastic modulus, greater than 1 TPa (the elastic modulus of diamond is 1.2 TPa) and reported strengths 10–100 times higher than the strongest steel at a fraction of the weight. Indeed, if the reported mechanical properties are accurate, carbon nanotubes may result in an entire new class of advanced materials. To unlock the potential of carbon nanotubes for appli￾cation in polymer nanocomposites, one must fully understand the elastic and fracture properties of carbon nanotubes as well as the interactions at the nanotube/ matrix interface. Although this requirement is no dif￾ferent from that for conventional fiber-reinforced com￾posites [3], the scale of the reinforcement phase diameter has changed from micrometers (e.g. glass and carbon fibers) to nanometers. In addition to the exceptional mechanical properties associated with carbon nanotubes, they also posses 0266-3538/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(01)00094-X Composites Science and Technology 61 (2001) 1899–1912 www.elsevier.com/locate/compscitech * Corresponding author. Tel.: +1-302-831-2421; fax: +1-302-831- 3619. E-mail address: chou@me.udel.edu (T.-W. Chou)