Optical limiting properties of suspended and solubilized carbon nanotubes

Full and shortened single-walled and multiple-walled carbon nanotubes were suspended in water to form stable suspensions in the presence of a surfacta nt. Optical limiting properties of the suspensions were determined for 532- nm pulsed laser irradiation, and the results were comparable with those of carbon black aqueous suspension. Solubilization of the shortened carbon nan otubes was achieved by attaching the nanotubes to highly soluble poly(propi onylethylenimine-co-ethylenimine) or by functionalizing the nanotubes with octadecylamine. The soluble carbon nanotube samples formed homogeneous solu tions in room-temperature chloroform. Optical limiting properties of these solutions were also determined for 532-nm pulsed laser irradiation, and the results were found to be quite different from those of the carbon nanotube aqueous suspensions. Apparently, the carbon nanotubes exhibit significantl y weaker optical limiting responses in homogeneous solutions than in suspen sions. Mechanistic implications of the experimental results are discussed.