Sensors Based on Multiwalled Carbon Nanotubes

Abstract

In this study, we exploit films of multiwalled carbon nanotubes (MWCNTs) as the sensing element of new and low-cost sensors for temperature, pressure and humidity. Aqueous solutions of functionalized MWCNTs are vacuum filtered to produce freestanding films of randomly oriented MWCNTs, known as buckypaper, with thickness in the range 200–500 µm. The electric resistance of the buckypaper, patterned in strips with widths of a few mm and lengths of up to a few cm, is investigated as a function of temperature, pressure and humidity. The electric resistance of the buckypaper shows a monotonic decrease for increasing temperature over the 80–380 K range. Owing to the high porosity, the buckypaper structure can be changed by the application of a force. A compressive force applied over the buckypaper surface improves the electric contact between the MWCNTs and results in a decrease in the electric resistance. The exposure of the buckypaper to liquid or vapour water increases its electric resistivity. The experimental data presented in this work confirm that the electrical conduction of a buckypaper is highly sensitive to environmental conditions and that the buckypaper is an interesting material with promising applications in a variety of low-cost sensors with high sensitivity and fast response.