The synergic regulation of conductivity and Seebeck coefficient in pure polyaniline by chemically changing the ordered degree of molecular chains

Pure polyaniline (PANI) films with different molecular chain packing states were successfully prepared by simply tuning the m-cresol content in the solvent. The SEM and AFM images display that the films are dense and smooth. The Vis-UV spectrum and Raman spectrum suggested that the conformation of PANI molecules changed from a compacted coil to an expanded coil by the chemical interactions between PANI and m-cresol, which enhanced the delocalization of pi-polarons along the polymer chain. The XRD analysis indicated that the PANI molecular chain with different ordered degrees formed during the solvent evaporation process. Furthermore, the measurement of temperature-dependent electrical conductivity confirmed that the ordered regions in PANI molecular structures were enhanced with increasing m-cresol content, which decreased the hopping barrier and increased the carrier mobility. Consequently, when the m-cresol content increased, the electrical conductivity increased remarkably, while the Seebeck coefficient maintained the same level or increased slightly. The experimental results clearly reveal the intrinsic effect of molecular structure on the electric transport of conducting polymers. It strongly suggests that increasing the ordered regions in the polymer molecular chain structure is an effective way to improve the thermoelectric properties of conducting polymers.