Effect of Protonating Phosphoric Acid-Based Dopants on the Electroconductive and Mechanical Properties of Polyaniline/Poly(2-acrylamido-2-methylpropanesulfonic acid) Complexes

This study aims to investigate the effects of using different small molecule dopants based on phosphoric acid such as nitrilotrimethylphosphonic acid (NTMPA), 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate (BNHP), and pyrophosphoric acid (PPA) in a polyaniline/poly(2-acrylamido-2-methylpropanesulfonic acid) (PANI/PAAMPSA) polymer complex. The impacts of the size, structure, and number of acid groups of these small molecule dopants on the resulting solvent-cast film properties are examined. The polymer film is synthesized through a templated oxidative polymerization of aniline, where the resulting complex is noncovalently bonded via hydrogen bonding and electrostatic interactions. Fourier transform infrared spectroscopy confirmed the presence of a greater degree of hydrogen bonding in the PANI/PAAMPSA/PPA film, resulting in a greater elongation at break (ε = 3750%) and higher water content (16.3%). The stronger hydrogen bonding in PANI/PAAMPSA/PPA created robust cross-linking within the material, which reduced its ability to self-heal. On the other hand, the PANI/PAAMPSA/NTMPA film achieved high self-healing efficiencies of 98% (conductive self-healability) and 77.3% (mechanical self-healability) due to its more dynamic hydrogen bonding and electrostatic interactions. Furthermore, PANI/PAAMPSA/BNHP showed less hydrogen bonding, stretchability, and self-healing capabilities due to the steric hindrance and hydrophobicity caused by its rigid bulky structure compared to the more linear structures of the other dopants investigated.