Functionalized polyanilines: influence of the surface morphology on the electrophysical and sensory properties of thin films based on them
The effect of the morphology of polyaniline (PANI) and its copolymers on the electrical conductivity and sensory sensitivity to air humidity of thin-film structures based on them has been studied. Polyaniline and three new related copolymers have been synthesized: poly (aniline-co-ortho-toluidine), poly{aniline-co-2-(cyclohec-2-en-1-yl)aniline}, poly{aniline-co-2- (cyclopent-2-en-1-yl)aniline}. Using a scanning electron microscope, the surface morphology of thin films obtained from a solution of synthesized polymers by spin coating on sitall substrates was studied. The morphology of the samples obtained from copolymers with ortho-toluidine and new PANI derivatives differs significantly from PANI itself, which indicates the effect of substituents on the supramolecular structure. Since high-molecular-weight samples were synthesized under identical conditions, the revealed differences in morphology are directly related to the mechanism of interaction of monomeric units. Large hollow spheres were obtained by the mechanism of self-assembly of a copolymer sample based on ortho-toluidine. It is known, that such a morphology is a potentially useful structure for obtaining various sensor devices. On the basis of PANI and its copolymers, samples of resistive thin-film structures were prepared and the dependence of their electrical conductivity on the value of the relative air humidity was measured. The influence of the surface morphology of PANI films and its copolymers on the sensor sensitivity to air humidity was experimentally revealed, and the prospects of using the studied films in humidity sensors were shown. It was found that at maximum values of relative air humidity of 90 %, films of poly(aniline-co-ortho-toluidine) copolymer had the highest conductivity. Samples of sensors based on unmodified PANI demonstrate the lowest conductivity. It should be noted that the resistive sensors on thin films of poly{aniline-co-2-(cyclohec-2-en-1-yl)aniline} have the most uniform and close to linear characteristic in the range of 20 - 90 % humidity.