Facile Optimal Synthesis of Inherently Electroconductive Polythiophene Nanoparticles

Polythiophene (PTh) nanoparticles were successfully synthesized by a simple chemical oxidative polymerization in the presence of a very small amount of cetyltrimethylammonium bromide (CTAB). The polymerization yield, particle size, bulk electrical conductivity, and solubility of the PTh nanoparticles have been optimized by adjusting the CTAB/FeCl3 oxidant/thiophene monomer ratio, thiophene concentration, polymerization temperature, and reaction time. The structure of the PTh nanoparticles was systematically characterized by IR and UV/Vis spectroscopy, wide-angle X-ray diffraction, laser particle-size analysis, field-emission scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the number-average diameter (D-n) and size polydispersity index (PDI) of the particles decrease significantly from 4.19 mu m and 1.21 to 203 nm and 1.056, respectively, with a slightly increasing CTAB concentration. SEM and TEM reveal that the PTh particle size is reduced to 67 and 36 nm, respectively. The conductivity increases on raising the FeCl3/thiophene ratio or on lowering the CTAB concentration and polymerization temperature. A moderate monomer concentration and polymerization time are very beneficial for achieving highly conducting PTh. The highest conductivity of virgin PTh is 3.1 x 10(-4) Scm(-1) and can be further elevated to 50 Scm(-1) by doping in iodine vapor. Under optimized polymerization conditions, the significant variation of the conductivity of the PTh particles in virgin and doped states was well confirmed by the intensity and wavelength of the UV/Vis spectral band owing to the large pi conjugation. The PTh particles demonstrate uncommon characteristics including easy synthesis, low cost of production, large pi-conjugated structure, high conductivity, solution processability, and extensive potential for further application.