Fluorinated Single Wall Nanotube/Polyethylene Composites for Multifunctional Radiation Protection
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Fluorinated Single Wall Nanotube/Polyethylene Composites for Multifunctional Radiation Protection Merlyn X. Pulikkathara1, Meisha L. Shofner2 , Richard T. Wilkins1, Jesus G. Vera2, Enrique V. Barrera2, Fernando J. Rodríguez-Macías3, Ranji K. Vaidyanathan4, Catherine E. Green4, Clay G. Condon4 1 Center for Applied Radiation Research, Prairie View A&M University, Prairie View, TX 77446, U.S.A. 2 Department of Mechanical Engineering and Material Science, Rice University, Houston, TX 77005, U.S.A. 3 Department of Chemistry, Rice University, Houston, TX 77005, U.S.A. 4 Advanced Ceramics Research, E. Hemisphere Loop, Tucson, AZ 85706, U.S.A. ABSTRACT Fluorinated Single Wall Nanotubes (f-SWNTs) have been processed in polyethylene by an incipient wetting technique to achieve a well dispersed nanocomposite for radiation protection. In some cases, samples were further processed using the rapid prototyping method of extrusion freeform fabrication. Composites were exposed to 40 MeV proton radiation with a flux of about 1.7x107 protons/cm2/sec to a total fluence of 3x1010 protons/cm2 .This exposure is consistent with a long-term space mission in low earth orbit. The samples were evaluated by means of Raman spectroscopy and thermogravimetric analysis (TGA). These results were compared to the unexposed composite and unfilled polymer samples. This study has focused on the stability of the nanotube composites when exposed to radiation and prior to hydrogen exposure. It was shown that the stability of the functional group is not constant with SWNTs produced by different processes and that radiation exposure is capable of defluorinating SWNTs in polyethylene. INTRODUCTION Since the discovery of single wall carbon nanotubes (SWNTs) in 1993 [1, 2], research has been conducted to exploit their unique mechanical, electrical, and thermal properties to create multifunctional composite materials [3]. Previous research has shown that SWNTs have the highest measured electrical conductivity of any known fiber [4], a higher thermal conductivity than diamond [5], and the highest stiffness of any known fiber [6]. Due to the provocative geometry and other remarkable properties of carbon nanotubes, they are of interest to the aerospace and radiation communities [7-10]. The possibility of nanotubes serving as a storage medium for hydrogen is of particular interest for future spacecraft, and hydrogen-rich and other low atomic mass materials are believed to minimize radiation exposure in the space environment [11]. It is expected that nanotube polymer composites will be effective radiation protection shielding when prepared to contain hydrogen. Fluorinated and purified SWNTs were used in this work to prepare polyethylene composites. Fluorination is seen as a near term approach for achieving un-roped nanotubes for composite applications, and it may even shorten the tube lengths. As an extension of the work presented in this paper, a sample of f-SWNT/polyethylene composite material was processed and further prepared by extrusion freeform fabrica
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