Kinetics of Photoactuation in Single Wall Carbon Nanotube-Nafion Bilayer Composite

Cantilevers made of a bilayer composite of single walled carbon nanotubes (SWNTs) deposited onto Nafion exhibit substantial mechanical motion upon exposure to visible or near-infrared light. The kinetics of the tip displacement are studied as a function of SWNT thickness, mass loading, and humidity level. The rate constants strongly depend upon the SWNT layer thickness. During the light-on cycle the absorption of the light by the SWNTs drives the motion while in the light-off cycle the stiffness of the SWNTs retards the relaxation. At low humidity levels a second, fast, but small, response in the opposite direction of the net major displacement is observed. The kinetics of the photoactuation was also monitored by IR spectroscopy with similar kinetic parameters. The primary mechanism responsible for the actuation appears to be migration of water and hydrated hydrogen ions in the Nafion film toward the interface and into the SWNT layer.