Morphology and Dopant Influence Electrical Properties and Stability of Multiwalled Carbon Nanotube-Polyaniline Composites

In situ chemical polymerization is used to prepare composites of multiwalled carbon nanotubes (MWCNTs) that are either wrapped with polyaniline (PANI) (MWP), or with perpendicular aligned PANI (MAP). Systematic study of morphology, composition, structure, thermal stability, and electrical properties is performed as a function of temperature to understand the composite formation. Orientation of PANI chains and the direction of electron transport in MWCNTs and PANI play an important role in conductivity. At room temperature (RT), MWP, wherein PANI and MWCNTs are aligned parallel, exhibits high conductivity, which decreases gradually above RT. Contrary in MAP, the conductivity at RT is lower because of the perpendicular alignment of PANI on the MWCNTs. However, it increases with the increase in temperature, as short chains of PANI switchover and get adsorbed onto the MWCNTs forming a near parallel orientation, in which, aromatic amines of PANI graft to the MWCNTs. Eventually, morphology becomes a dominating factor which influences the conductivity and thermoelectric properties of the composites, above 150 °C. The results show that the morphology, interfacial contact, and the dopant concentration are the key factors in governing the conductivity of MWP and MAP composites at RT and above. These observations are supported by X-ray diffraction, X-ray photoelectron spectroscopy, and time of flight-secondary ionization mass spectrometry study.