Fabrication of oriented polyaniline nanostructures using block copolymer nanotemplates and their optical, electrochemical and electric properties

Abstract

Arrays of oriented polyaniline (PANI) nanostructures of different shape and size were fabricated on transparent ITO substrates using block copolymer nanotemplate as scaffold material. Polyaniline in these nanostructures was synthesized by electropolymerization. The electrochemical deposition requires only a single step where the size and shape of the nanostructures vary with time and can be tailored easily. Both AFM and SEM studies were carried out in order to study the morphology of different polyaniline nanostructures fabricated using block copolymer nanotemplates. SEM investigations confirm that the morphology of fabricated polyaniline nanostructures is different from the polyaniline simply grown on blank ITO using the same experimental conditions. The optical, electrical and electrochemical properties of these polyaniline nanostructures have been studied. These polyaniline nanostructures show different optical and electrochemical properties as compared to randomly grown polyaniline thin film on blank ITO. Polyaniline nanostructures fabricated using block copolymer templates have an additional absorption peak near 510 nm which is due to different chain conformations of polyaniline growing inside the block copolymer template. The polyaniline deposited using the block copolymer nanotemplate has additional redox peaks as compared to polyaniline deposited on bare ITO. The presence of an extra redox couple (around 0.515/0.487 V) clearly indicates that polyaniline nanostructures have some quinone type defect which is absent in the polyaniline deposited on bare ITO. We have studied the electric properties of these polyaniline nanostructures using conducting AFM. The discrete bright spots in the current image indicating the areas where current flows, correspond to the individual polyaniline nanostructures. In contrast, the current image of the polyaniline film prepared on blank ITO, indicates that polyaniline covers the entire surface.