Mechanisms of polyaniline film formation via solution casting: Intra-chain contraction versus inter-chain association

• Mechanisms of formation of solution-cast films of polyaniline are dependent on the solution concentration. • Formation of “blue” films is due to entanglement of polymer chains of expanded conformation. • Formation of “violet” films is due to intra-chain compact coil conformation. • Higher amount of solvent residue, better protonation and absorption of analyte vapors for “blue” films. Two different mechanisms of formation of solution-cast films of emeraldine base (EB) of polyaniline are shown. The first mechanism was found in films drop-cast from the concentrated solution of EB. This mechanism is suggested to be due to entanglement of different polymer chains when the film is formed. It results in the relatively loose film morphology with fractal dimensionality of 1.68 and blue color. This film has a relatively good ability to absorb analyte vapors from the environment and a better ability to be protonated from the acidic medium as compared to films formed by the second mechanism. It is suggested that the polymer has an extended coil conformation in such a film, similar to that in a good solution. The second mechanism takes place when the film is drop-cast from a solution of low concentration and it is controlled by intramolecular processes which play the major role before the molecules aggregate into the film. This mechanism is suggested to be due to prevailing intramolecular tendency to compact-coil conformation. It results in formation of films of the grained morphology with fractal dimensionality of 1.56 and violet color. These films have a poor ability for absorption of analyte vapors and protonation as well. Various factors that affect the above mechanisms are discussed. The different properties of the films resulted from the different formation mechanisms allow us to specify them as different polymer phases, where either inter- or intra-chain processes play a crucial role, respectively.