The role of carbon nanotubes on the sensitivity of composites with polyaniline for ammonia sensors

In this work we present morphological and thermal studies on the behaviour of ammonia gas sensor devices fabricated with neat polyaniline (PANI) polymer and different ratios of polyaniline and multiwalled carbon nanotubes (MWCNT:PANI) films as active layer. The inclusion of MWCNT improved the devices stability and lifetime, acting as a drain of thermal energy, and present better stability when compared with devices based on polymer only. The interdigitated MWCNT:PANI devices showed strong electrical response dependence on the morphology of the films with optimum efficiency for certain combination of the materials. The morphology changes according to the size of the nanotubes and the size of the polymer clusters formed in the PANI films. We treat the composite material as a collection of resistors entangled in a heavily disordered network, which can be described by two characteristic resistance values, following recent results based on the Effective Medium Theory. We propose a plausibility argument based on scaling factors for the resistance of the network components which points to the appearance of an optimal sensitivity as a function of the polymer-nanotube ratio.