posted on 2014-10-02, 00:00authored byManel Canales, Juan Torras, Georgina Fabregat, Alvaro Meneguzzi, Carlos Alemán
The polaronic and bipolaronic forms
of polyaniline emeraldine salt
(PAni-ES) in the amorphous solid state have been simulated using classical
molecular dynamics (MD) and hybrid quantum mechanical/molecular mechanical-molecular
dynamics (QM/MM-MD) approaches. It should be remarked that the electronic
state of PAni-ES has been theoretically investigated in the gas phase,
solution phase, and crystalline state, but this is the first study
in the amorphous solid state, which is the most typical for this conducting
polymer. MD simulations were carried out using force-field parametrizations
explicitly developed for polaronic and bipolaronic models. QM/MM-MD
calculations were performed using a quantum mechanical zone defined
by four repeat units. In addition of the structural and electronic
characteristics of the two forms of PAni-ES, MD and QM/MM-MD simulations
indicate that the bipolaronic is the most stable state of amorphous
PAni-ES. Complementary studies have been carried out using different
experimental techniques. Although the morphology and topography of
doped and undoped PAni are very similar, comparison of their UV–vis
spectra supports the preference toward the bipolaronic form of PAni-ES.