Carbon Nanotube network based sensors

We demonstrate three types of sensors based on spray-deposited Carbon Nanotube (CNT) networks on flexible substrates: humidity sensors, dew-point sensors and time-temperature indicators. The presence of Sodium Dodecylsulphate (SDS) significantly increases the sensitivity of the film resistance of CNT networks to changes of relative humidity. We observe up to a 3% change in film resistance in the 30-75% range of relative humidity, with a non-linear relationship. When these SDS-impregnated CNT films are cooled to the dew-point of air, with the temperature of the film monitored, the associated increase in sheet resistance can be used to establish the dew-point temperature. We use acid-doped CNT networks as time-temperature indicators, exploiting the de-doping of the CNT networks at higher temperature. We observe an increase in film resistance of such networks at temperatures higher than 50°C. The rate of the resistance increase follows the Arrhenius law. The extent of the resistance increase ranges from ~30%at 50°C to >;300% at 100°C.