Physical Interactions of Carbon Nanotubes and Conjugated Polymers
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Physical Interactions of Carbon Nanotubes and Conjugated Polymers A.B. Dalton1, B. McCarthy2, JN Coleman2,M in het Panhuis2, D. L. Carroll3, R. Czerw3, W.J. Blau2, H.J. Byrne1 1
FOCAS/School of Physics, Dublin Institute of Technology, Dublin 08, Ireland Physics Department, Trinity College Dublin, Dublin 2, Ireland 3 Department of Physics and Astronomy, Clemson University, South Carolina, USA
2
ABSTRACT Single walled carbon nanotubes are shown to interact with a conjugated polymer in a periodic manner. Here this interaction is probed using electron microscopy, scanning tunneling microscopy optical and vibrational spectroscopy. The spectroscopic behaviour of the polymer is seen to be dramatically affected, which is attributed to conformational changes due to the effect of the nanotubes. INTRODUCTION Since the discovery of carbon nanotubes in 1991[1], researchers have envisaged potential applications such as nanoscale electronic circuits and the construction of complex carbon-based nano-machines. Thus, the assembly of basic building blocks of complex nano-architectures, such as conjugated polymers and nanotubes, has been a driving goal of much of the nano-science community. A first step toward realizing this goal may be the attachment to, or modification by carbon nanotubes of structures such as polymers. This leads to the possibility of assembling individual polymer molecules onto carbon nanotubes with the net effect being the modification of the polymer’s electronic properties and structure in a predictable way. To accomplish this, clearly, a more detailed understanding of the interactions between conjugated polymers and carbon nanotubes must be sought. In this work, we describe the assembly of the polymer, poly(m-phenylenevinylene-co-2,5-dioctoxy-p-phenylenevinylene), (PmPV), into a coating around single walled carbon nanotubes, (SWNT). Electron microscopy, scanning tunneling microscopy and Raman spectroscopy indicate that the polymer backbone interacts with the lattice of the nanotubes. This results in pronounced alterations to the fluorescence and absorption characteristics. This is explained as a reduction in electron delocalisation due to the affected polymer conformation, and also a dilution of aggregation effects. EXPERIMENTAL Synthesis of the polymer has been described previously[2]. Notable about this polymer are the dioctyloxy sidegroups, which impose a linear, exposed structure onto the PmPV backbone thus allowing significant interaction with the lattice of nanotubes. SWNT were produced in a generator using the arc discharge technique[3]. Composite preparation is relatively simple; SWNT are added to a solution (typically in this case 1g/L) of PmPV in toluene. Nanotube aggregates are broken up by briefly exposing the composite solution to a high power sonic tip (3 minutes), and then sonicating for several hours in a low power sonic bath. Due to the strong tendency of SWNT to aggregate, relatively low mass fractions of SWNT to PmPV can be W4.5.1
achieved (typically 2-3%). In this case, to achieve as hig
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