Electron Spin Resonance Studies on Electron Beam Irradiated Carbon Nanotubes Dispersed in Styrene-Isoprene-Styrene Block
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Electron Spin Resonance Studies on Electron Beam Irradiated Carbon Nanotubes Dispersed in Styrene-Isoprene-Styrene Block Copolymer Mircea Chipara1, Wendland Beezhold2, Timothy Webb2, Jeffrey M. Zaleski4, Kristina Stephenson4, David Dye4, Kin-Tak Lau3 1 Indiana University Cyclotron Facility, Indiana University, Bloomington, Indiana 2 Physics Department, Idaho State University, Pocatello, Idaho 3 Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong 4 Chemistry Department, Indiana University, Bloomington, Indiana.
ABSTRACT Electron spin resonance investigations on the effect of electron bombardment of nanocomposites obtained by dispersing carbon nanotubes within styrene-isoprene-styrene are reported. The experimental results revealed the absence of radiation-induced free radicals and a negligible effect of electron beam irradiation on the electron spin resonance spectra of carbon nanotubes.
INTRODUCTION The composites based on carbon nanotubes have a particular importance for space applications due to their multifunctional characteristics. Besides the reduced weight of the polymeric matrix that decreases the payload and reduces space mission costs, the introduction of carbon nanotubes enhances the mechanical strength of the polymeric matrix. The outstanding mechanical properties of carbon nanotubes are exploited in composite materials through the load transfer from the polymeric matrix to carbon nanotubes. Up to now, Raman spectroscopy is the most appropriate techniques for the investigation of the load transfer from the polymeric matrix to carbon nanotubes [1-3]. The adhesion between nanotubes and polymeric matrices, important in increasing the structural properties of polymeric matrices, is not yet fully understand. The introduction of carbon nanotubes is also affecting the thermal and electric conductivity of the polymeric matrix. For carbon nanotubes with a high aspect ration the percolation threshold for DC conductivity has been reported to be lower than 0.5 % weight [4-5]. Hence, minute amounts or nanotubes are capable of inducing antistatic and even electrical conducting features. Experimental data revealed that the dispersion of nanotubes in polymeric matrices shifts the glass and melting temperatures to higher temperatures. However, the effect of carbon nanotubes on the thermal stability of polymers is still under debate. Recent experimental showed that the introduction of nanotubes within polymers reduces their thermal stability [6]. The radiation stability of polymeric composites based on carbon nanotubes was not yet assessed. From the theoretical standpoint, carbon nanotubes are expected to have an outstanding resistance to ionizing radiation. This derives from the conducting features of carbon nanotubes and from the strong interactions between conduction electrons and between conduction electrons and phonons. Accordingly, the energy deposited within
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carbon nanotubes by the incident ionizing radiation is rapidly dispersed. While it was reported that electron [7] or
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