Layer-by-layer assembly and humidity sensitive behavior of poly(ethyleneimine)/multiwall carbon nanotube composite films

Raw CVD grown multiwall carbon nanotubes (MWCNTs) were oxidized in a mixture of concentrated sulfuric acid and nitric acid to obtain water soluble MWCNTs. Composite multilayer films of the oxidized MWCNTs and poly(ethyleneimine) (PEI) were fabricated through the layer-by-layer (LbL) assembly approach. The oxidized MWCNTs were characterized with Fourier transform infrared spectroscopy. The LbL assembly process of the multilayer films was monitored with a UV-vis spectrophotometer. The surface and sectional morphology of the films were observed under a Schottky field emission scanning electron microscope. On the assembled thin films, two parallel metal electrodes were vapor deposited. The resistance between the two electrodes was measured at different relative humidity levels at room temperature. The data show that the resistance increases with increasing the relative humidity over the range of 5-97% RH and that, in the range of 5-85% RH, the resistance increases almost linearly. The experimental data also show that the humidity sensitive multilayer films have response and recovery times of about 2 and 30 s, respectively. (c) 2006 Elsevier B.V. All rights reserved.