Effect of processing temperature on thermal doping of polyaniline without shear

Abstract

Electrically conducting samples of polyaniline (PANI) were prepared by doping with dodecylbenzene sulfonic acid (DBSA) using a thermal doping method without the application of shear. Besides characterizing the samples using optical microscopy, SEM, UV-vis-NIR, the degree of doping and the electrical conductivity were also measured. The pure PANI powder consisted of aggregates of PANI particles and was non-conducting. In the shear-free thermal doping of the PANI/DBSA mixture, the original aggregates were progressively broken up into smaller pieces with increasing temperature while maintaining the original primary particle shape and size and which were dispersed rather uniformly in the DBSA matrix. The electrical conductivity of doped PANI increased with increasing doping temperature. This increase strongly mirrored the increase in the levels of DBSA directly associated with PANI and suggested that the increasing levels of PANI doping were directly responsible for the increase in electrical conductivity as a function of the doping temperature. Despite the absence of the absorption peak at around 800nm, the sample absorbed strongly in the near-infrared. Moreover, PANI/DBSA samples possessing a higher ratio of absorbance at 2600nm to that at 800nm showed higher electrical conductivity. These results suggest that shear-free thermal doping provides a simple route to controlling the morphology of the mixture by enabling the disintegration of the micron scale aggregates present in the as-purchased PANI. This in turn can be used to control the degree of doping of the PANI and consequently the conductivity of the sample. © 2011 John Wiley & Sons, Ltd.