The Effect of Nanotube Loading and Dispersion on the Three-Dimensional Nanostructure of Carbon Nanotube-Conducting Polym
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The Effect of Nanotube Loading and Dispersion on the Three-Dimensional Nanostructure of Carbon Nanotube-Conducting Polymer Composite Films Mark Hughes,* George Z. Chen, Milo S. P. Shaffer, Derek J. Fray and Alan H. Windle Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK. ABSTRACT Nanoporous composite films of multi-walled carbon nanotubes (MWNTs) and either polypyrrole (PPy) or poly(3-methylthiophene) (P3MeT) were grown using an electrochemical polymerization technique in which the nanotubes and conducting polymer were deposited simultaneously. The concentration and dispersion of MWNTs in the polymerization electrolyte was found to have a significant effect on the thickness of polymer coated on each MWNT and hence the loading of MWNTs in the films produced. It has been shown that for an increasing concentration of MWNTs in the polymerization electrolyte, the thickness of polymer coated on each MWNT decreases. This relationship made it possible to minimize ionic diffusion distances within the nanoporous MWNT-PPy films produced, reducing their electrical and ionic resistance and increasing their capacitance relative to similarly prepared pure PPy films. INTRODUCTION The electrochemical growth of carbon nanotube-conducting polymer composites offers the ability to produce three-dimensional nanostructured films that combine the redox charge storage mechanism of conducting polymers with the high surface area and conductivity of carbon nanotubes [1-3]. This desirable merging of properties presents new opportunities to produce superior materials for applications such as supercapacitors, sensors and actuators. Given the bearing that the nanostructure of these composite films has on their electrochemical properties, it is important to develop an understanding of how the film structure can be controlled via manipulation of the growth conditions. In this way, it becomes possible to take full advantage of the remarkable properties of these composite films by tailoring their nanostructure as required. The work described here relates to electrochemically grown composite films of multi-walled carbon nanotubes and conducting polymers (PPy and P3MeT) and the influence of carbon nanotube loading and dispersion on their structure and electrochemical behavior. EXPERIMENTAL DETAILS Carbon nanotube-conducting polymer composite films were grown using an electrochemical method in which MWNTs and either PPy or P3MeT were simultaneously deposited on a graphite disk working electrode (0.33 cm2) in a single compartment cell. A graphite rod (0.65 cm diameter) counter electrode was used in combination with either a saturated calomel reference electrode (SCE) or a silver wire pseudo-reference electrode with the choice of reference electrode depending on the polymerization electrolyte used. Electrochemical synthesis was performed using a Model 273A EG&G Princeton Applied Research Potentiostat-Galvanostat. When growing composite films of MWNTs and PPy, an aqueous polymerization e
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