Electrical and optical properties of ceramic-polymer nanocomposite coatings

Transparent, conductive composite coatings were fabricated from suspensions of poly(vinyl acetate-acrylic) (PVAc-co-acrylic) copolymer latices (50-600 nm) and nanosized antimony-doped tin oxide (ATO) particles (∼15 nm). The suspensions were deposited as coatings onto poly(ethylene terephthalate) substrates and dried at 50 °C. Microstructure studies using field emission scanning electron microscopy and tapping-mode atomic force microscopy (TMAFM) indicated that the latex particles coalesced during drying and forced the ATO particles to segregate into the boundaries between the latex particles. Low phase contrast was observed with TMAFM; this result was consistent with the presence of PVAc-co-acrylic in the ATO-rich phase of the composite. The conductivity of the composite coatings followed a percolation power-law equation, with the percolation threshold between 0.05 and 0.075 volume fractions of ATO and the critical conductivity exponent ranging from 1.34 to 2.32. The highest direct-current conductivity of the composite coatings was around 10^-2 S/cm. The optical transmittance and scattering behavior of the coatings were also investigated. Compared with the PVAc-co-acrylic coating, the composite coatings had lower transparency because of the Rayleigh scattering. The transparency of the composite coatings was improved by a reduction in the coating thickness. The best transparency for the coatings with a direct-current conductivity of approximately 10^-2 S/cm was around 85% at a wavelength of 600 nm.