Carbon Nanotube Electroactive Polymer Materials: Opportunities and Challenges
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Electroactive Polymer Materials: Opportunities and Challenges
Liangti Qu, Qiang Peng, Liming Dai, Geoffrey M. Spinks, Gordon G. Wallace, and Ray H. Baughman Abstract Carbon nanotubes (CNTs) with macroscopically ordered structures (e.g., aligned or patterned mats, fibers, and sheets) and associated large surface areas have proven promising as new CNT electroactive polymer materials (CNT-EAPs) for the development of advanced chemical and biological sensors. The functionalization of CNTs with many biological species to gain specific surface characteristics and to facilitate electron transfer to and from them for chemical- and bio-sensing applications is an area of intense research activity. Mechanical actuation generated by CNT-EAPs is another exciting electroactive function provided by these versatile materials. Controlled mechanical deformation for actuation has been demonstrated in CNT mats, fibers, sheets, and individual nanotubes. This article summarizes the current status and technological challenges for the development of electrochemical sensors and electromechanical actuators based on carbon nanotube electroactive materials.
Introduction Carbon has long been known to exist in three forms: amorphous carbon, graphite, and diamond.1 The Nobel-Prize–winning discovery of buckminsterfullerene C60 in 1985 created an entirely new branch of carbon chemistry.2,3 The subsequent discovery of carbon nanotubes (CNTs, Figure 1a) in 1991 opened a new era in materials science and nanotechnology.4 As can be seen in Figure 1b, a CNT may be conceptually viewed as a graphite sheet that is rolled into a nanoscale tube form as a singlewalled carbon nanotube (SWNT), or as a multiwalled carbon nanotube (MWNT) with additional graphene coaxial tubes around the SWNT core.5 Depending on their diameter and the helicity of the orientation of graphite
rings along the nanotube length, CNTs can exhibit semiconducting or metallic behavior to allow them to be used for many potential applications,5 including as new electroactive polymers (CNT-EAPs) in advanced composite systems, singlemolecular transistors, molecular computing elements, field-emitting flat-panel displays, sensors, and artificial muscles. In this article, we summarize the current status and the remaining technological challenges for the development of advanced CNT-EAP materials, with a focus on their use as sensors and actuators.
Carbon Nanotube EAPs Conjugated polymers with alternating single and double carbon–carbon bonds
MRS BULLETIN • VOLUME 33 • MARCH 2008 • www.mrs.org/bulletin
have been demonstrated to possess interesting optoelectronic properties through a continuous overlapping of π-orbitals along the polymer backbone.6,7 The overlap of π-orbitals opens a channel of charge transport along the polymer backbone to provide tunable electronic properties. These properties make conjugated polymers attractive for use as electroactive polymers (π-EAPs) in various sensing and actuation devices. Having a well-defined conjugated all-carbon one-dimensional structure, CNTs are p
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