Effects of gamma radiation on poly(methyl methacrylate)/single-wall nanotube composites
- PDF / 203,405 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 203 Views
K. Sikder and A. Kumar Center for Microelectronics Research, University of South Florida, 4202 E Fowler Avenue, Tampa, Florida 33620-5250
A.M. Cassell and M. Meyyappan NASA Ames Research Center, Moffett Field, California 94035 (Received 10 April 2002; accepted 27 June 2002)
Single-wall carbon nanotube (SWNT)/poly(methyl methacrylate) (PMMA) composites were fabricated and exposed to ionizing radiation for a total dose of 5.9 Mrads. Neat nanotube paper and pure PMMA were also exposed for comparison, and nonirradiated samples served as controls. A concentration of 0.26 wt% SWNT increased the glass transition temperature (Tg), the Vickers hardness number, and modulus of the matrix. Irradiation of the composite did not significantly change the Tg, the Vickers hardness number, or the modulus; however, the real and imaginary parts of the complex permittivity increased after irradiation. The dielectric properties were found to be more labile to radiation effects than mechanical properties.
I. INTRODUCTION
Carbon nanotubes (CNTs) were discovered in 1991 by Ujima,1 and subsequently, interest has focused on exploiting their novel electronic and mechanical properties on a macroscopic scale. Nanotubes are concentric graphitic cylinders closed at either end due to the presence of five-membered rings.2 Carbon nanotubes exist in both multiwalled and single-walled forms. Multiwalled nanotubes (MWNTs) have a central tubule surrounded by outer shells.3 A single-wall carbon nanotube (SWNT) can either be metallic or semiconducting depending on its diameter and chirality;4,5 one-third of all carbon nanotubes are metallic, whereas the other two-thirds are semiconducting. Multiwalled carbon nanotubes have been shown to have an axial Young’s modulus of 200– 4000 GPa, a bending strength of 14 GPa, and axial compression strength of about 100 GPa.6–9 The high aspect ratio, mechanical strength, and high modulus of carbon nanotubes have led to the design and characterization of novel composites of carbon nanotubes in a series of host polymer matrices.10–15 Various methods have been used to fabricate polymer/carbon nanotube composites: solution mixing of polymer and
a)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 10, Oct 2002
http://journals.cambridge.org
Downloaded: 09 Dec 2014
carbon nanotubes;10 a combination of sonication and melt processing;11 melt blending;12 in situ polymerization in the presence of nanotubes.13 The chemical modification of nanotubes further broadens their uses in polymeric composites. Experimental results indicate that certain free-radical initiators open bonds in carbon nanotubes. Indeed, when present during the addition polymerization of methyl methacrylate, carbon nanotubes have been shown to participate in the polymerization process.13 Also, electron and ion beam irradiation of nanotubes has been shown to cause amorphization and dimensional changes. In some instances, irradiation appears to be responsible for “soldering” nanotubes to form mechanica
Data Loading...
