Fabrication and Characterization of Conductive Polyaniline Fiber

We previously reported the concept of `gel-inhibitor' assisted processing of ultra-high molecular weight emeraldine base (EB) into wet-spun fiber. This method uses small amounts of secondary amine additives, e.g., 2-methyl aziridine (2MA), to form thermodynamically stable, particle-free, and highly concentrated (20% w/w) EB solutions. 2MA is a relatively toxic compound. Here we report that wet-spun fibers with similar physical characteristics may be obtained by utilizing non-toxic heptamethyleneimine (HPMI) as the gel inhibitor. As-spun EB fiber was prepared and then subsequently immersed in a variety of different Bronsted acids. Room temperature DC conductivity values for the doped fibers ranged from 3 to 10^-5 S/cm depending on the acid dopant. The as-spun fibers were of low density and they contained closed-cell porous microstructures riddled with macro-voids due to residual solvent entrained during coagulation. Each fibers diameter was observed to either contract or expand depending upon which acid was used for doping the fiber segment. We also report the observed differences in fiber density, mechanical strength and conductivity as a function of the acid type selected for doping studies. Optical spectroscopy of the solutions used to prepare fiber with HPMI showed no evidence for polymer degradation. The thermal and mechanical properties of the as-spun and doped EB fibers are presented.