Recent Advances in Research on Carbon Nanotube–Polymer Composites By Michele T. Byrne and Yurii K. Gun’ko* 1. Introduction The area of carbon nanotube (CNT)–polymer composites has been progressing extremely rapidly in recent years. Nanotubes themselves have remarkable electrical, thermal, and mechanical properties. For example, CNTs theoretically have exceptional mechanical properties such as elastic modulus and strengths 10–100 times higher than the strongest steel at a fraction of the weight. In 2000, Yu et al. measured Young’s moduli values for individual multi-walled nanotubes (MWNT) of between 0.27–0.95 TPa, strengths in the 11–63 GPa range, and a toughness of 1240 J g 1 . [1] For single-walled nanotubes (SWNT), Young’s moduli were found to be in the range of 0.32–1.47 TPa and strengths between 10 and 52 GPa with a toughness of 770 J g 1 . [2] CNTs also show unique electrical properties and electric-current-carrying capacity 1000 times higher than copper wire. [3] Frank et al. calculated the conductance of an average nanotube to be 1/12.9 kV 1 . [4] This combination of properties makes CNTs potentially ideal candidates for the formation of polymer composites with improved mechanical properties and electrical conductivity. CNT–polymer composites have a multitude of potential applications ranging from ultrastrong materials for bullet-proof vests, to flexible displays, and electronic paper. [5] Adding carbon-based fillers to polymers to improve mechanical properties, decrease weight, and act as heat conductors is not a novel idea. Carbon black has been widely utilized to reinforce rubber and plastics, for example, it is extensively used in racing tires to reduce thermal damage. Carbon fibers are also hugely popular industrial materials that are used in cars, airplanes, bicycles, etc. However, the carbon-based polymer additives with the greatest poten- tial are CNTs. The ability to harness the mechanical strengths of CNTs has already given rise to new industrial products. For example, sports equipment, such as tennis racquets and golf clubs containing CNTs, has been produced and marketed. With CNTs becoming easier to produce and cheaper to buy, the CNT industry could potentially overtake that of the carbon fiber industry and become one of the major additives for polymer-composite fabrication. There are a number of reviews on the conductive and mechanical properties of CNT–polymer composites. [6–18] How- ever, a significant progress has been made in the area of the preparation and utilization of nanotube–polymer composite materials lately. In this Progress Report, we will explore how CNT–polymer composites have been developed in recent years, with particular attention to their mechanical and electrical (conductive) properties. 2. Functionalization of Carbon Nanotubes for Polymer-Composite Preparation The chemical functionalization of CNTs has been a subject of several reviews. [19–23] Here, we are going to focus only on recent developments of functionalization of CNTs for polymer compo- site formation. It is known that nanotube solubility, dispersion, and stress transfer must all be maximized to reach optimum mechanical properties. Unless the interface between nanotube and polymer is carefully engineered, poor load transfer between nanotubes, when in bundles, and between nanotubes and surrounding polymer chains may result in interfacial slippage. [24] PROGRESS REPORT www.advmat.de www.MaterialsViews.com [*] Prof. Y. K. Gun’ko, M. T. Byrne School of Chemistry and CRANN Istitute, Trinity College Dublin Dublin 2 (Ireland) E-mail: igounko@tcd.ie DOI: 10.1002/adma.200901545 Carbon nanotubes (CNTs) demonstrate remarkable electrical, thermal, and mechanical properties, which allow a number of exciting potential appli- cations. In this article, we review the most recent progress in research on the development of CNT–polymer composites, with particular attention to their mechanical and electrical (conductive) properties. Various functionalization and fabrication approaches and their role in the preparation of CNT–polymer composites with improved mechanical and electrical properties are dis- cussed. We tabulate the most recent values of Young’s modulus and electrical conductivities for various CNT–polymer composites and compare the effectiveness of different processing techniques. Finally, we give a future outlook for the development of CNT–polymer composites as potential alternative materials for various applications, including flexible electrodes in displays, electronic paper, antistatic coatings, bullet-proof vests, protective clothing, and high-performance composites for aircraft and automotive industries. 1672 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Mater. 2010, 22, 1672–1688