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IONIZING RADIATION EFFECTS ON INTERFACES IN CARBON NANOTUBE-POLYMER COMPOSITES Julie P. Harmon1, Patricia Anne O. Muisener1, LaNetra Clayton1, John D’Angelo1, Arun K. Sikder2 and Ashok Kumar2 Meyya Meyyappan3 and Alan M. Cassell3 1

Department of Chemistry Center for Microelectronics Research University of South Florida, 4202 E Fowler Avenue, Tampa, FL 33620-5250 3 NASA Ames Research Center, Moffett Field, CA 94035 2

ABSTRACT The purpose of this research was to probe nanotube-polymer composites for evidences of radiation induced chemistry at the interface of the host polymer and the nanotube structures. Single wall carbon nanotube (SWNT) / poly (methyl methacrylate) (PMMA) composites were fabricated and exposed to gamma radiation with a Co60 source at a dose rate of 1.28 X 106 rad/hour in an air environment for a total dose of 5.9 Mrads. Neat nanotube paper and neat PMMA were also exposed. Spun coat films of SWNT/PMMA were exposed to gamma radiation with a Ce157 at a dose rate of 4.46 x 103 rad/hr for a total dose of 3.86 Mrads. Both irradiated and non-irradiated samples were compared. Glass transition temperatures were characterized by differential scanning calorimetry. Dynamic mechanical analysis and dielectric analysis evidenced changes in relaxations induced by irradiation. Irradiated composites exhibited radiation induced chemistry distinct from degradation effects noted in the pure polymer. Scanning electron microscopy provided images of the SWNTs and SWNT/PMMA interface before and after irradiation. This investigation imparts insight into the nature of radiation induced events in nanotubes and nanocomposites.

INTRODUCTION Since the discovery of carbon nanotubes in 1991, interest has focused on exploiting their novel electronic and mechanical properties on a macroscopic scale in polymer composites[1]. Nonlinear optical (NLO) properties of nanotube composites have applications in optical sensor technology [2]. Nanotubes are of great interest in EMI shielding applications and in the design and development of nanoscale electronic devices [3,4]. Their high aspect ratio, mechanical strength and high modulus have prompted scientists to design and characterize novel composites of carbon nanotubes embedded in a series of host polymers [5-9]. Such ultra-strong, low-density, carbon nanotube composites demonstrate extraordinary potential for structural design in the building and automotive industry. Nanotube composites also exhibit potential applications in space environments where low-density structural materials must also survive exposure to ionizing radiation. The chemical modification of nanotubes further broadens their uses in polymeric composites. Experimental results indicate that certain free radical initiators open π bonds P9.7.1

in carbon nanotubes. Indeed, when present during the addition polymerization of methyl methacrylate, carbon nanotubes have been shown to participate in the polymerization process [10]. Several studies show that electron and ion beam irradiation of nanotubes gives rise to amorphizati