Characterizing the oxidation level of polyaniline (PANI) at the interface of PANI/TiO2 nanoparticles under white light illumination

• Interface of PANI/TiO2 was studied using microscopic and spectroscopic techniques.
• Observation of halo surrounds the particles shows the oxidation of PANI.
• Extent of dispersion of TiO2 particles, defines the oxidation level of PANI.
• Characterization of oxidation was done by chemical treatment and FTIR of composite films.
• Quantitative estimation was done by Raman spectroscopy.

The polymer/nanoparticle interface of polyaniline (PANI)/TiO2 composite was characterized by using Fourier transform infra-red spectrometer imaging system, Raman (both coupled with optical microscope) and UV–vis spectroscopy. During characterization, as white light from the optical microscope impinges on TiO2, it absorbs supra band-gap photons and electron-hole pairs are produced. On accepting the holes, PANI gets oxidized from emeraldine salt form to its next oxidation state that is pernigraniline salt form, leading to a change in color. In optical micrographs this change in color appears as a halo around each TiO2 particle and defines the extent of the oxidized area of PANI, which helps to characterize the extent of oxidation of PANI at the interface of PANI/TiO2. Further studies revealed that the range and extent of oxidation at the interface in polymer depend on the types of dispersions of TiO2 nanoparticles in PANI matrix.