Annealing Effects of Dilute Polyaniline/NMP Solution

Abstract

The annealing effects of a dilute polyaniline solution on chemical and physical properties were investigated. Emeraldine base (EB) of polyaniline prepared by the conventional procedure was dissolved in 1-methyl-2-pyrrolidinone (NMP). After heating at 60−140 °C for 2 h, the color of PANi solution changed from deep blue to various colors depending on the annealing temperature. This solution was filtered and cooled at −5 °C to preserve an undoped structure. Changes of physical and chemical properties were investigated using ultraviolet−visible (UV−vis), Fourier transform infrared (FT-IR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), and dynamic light scattering (DLS). By contrast to the previously reported reductive reaction, we concluded that the annealing of dilute EB/NMP solution resulted in cross-linking. This was indicated by the decrease of the mutual diffusion coefficient at infinite dilution (D0) and the increase in the apparent hydrodynamic radius (Rh) of EB with the annealing temperature evidenced by the DLS and the increase of the cyclic-N portion from ESCA results. The annealing also produces a polyelectrolyte chain, supported by FT−IR and DLS measurements.