n 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 width of few mm and length up to 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 4.2 - 420 K range. This feature is exploited to fabricate temperature sensors with high sensitivity and fast response. 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 of the electric resistance. It has been observed that the change can be reversible over a certain pressure range, thus enabling the use of the buckypaper as a pressure sensor. The exposure of the buckypaper to liquid or vapour water increases its electric resistivity. Hence, a MWCNT film is also suitable as humidity sensing purposes.

The experimental data presented in this work confirm that the electrical conduction of a buckypaper is highly sensitive the environmental conditions and that the buckypaper is an interesting material with promising applications in a variety of sensors.