The transparent conductive oxygen barrier graphene oxide film deposited via a self-assembly coating method
This study characterized the properties of a transparent oxygen barrier film in which graphene oxide (GO) was used as the barrier material. GO was produced by oxidizing graphite via chemical methods. Alternating self-assembled solution-deposited GO layers and poly(ethylenimine) (PEI) layers were then deposited on a PET film surface. GO produced by a modified Hummers’ methods was dispersed in distilled water, and was deposited onto PET films using a LBL deposition method. The negatively charged GO and positively charged PEI layers were alternately deposited on a PET film. The light transmittance of the GO/PEI LBL deposited film was 89.4% at 550 nm for the 5-bilayer GO/PEI.
The light transmittance and sheet resistance were measured as a function of the thermal treatment time in a convection oven at 150°C and UV exposure. The light transmittance of the deposited film without thermal treatment was 89.4%. This value decreased to about 62% after 20 minutes of thermal treatment, after which the film light transmittance was constant. The sheet resistance of the deposited film without heat treatment exceeded 10 MΩ/sq, the maximum sensitivity of the instrument. As the heat treatment time increased beyond 30 minutes, the sheet resistance decreased to about 2 MΩ/sq after 55 minutes. UV exposure accelerated the reduction of GO and yielded similar light transmittance and sheet resistance values. After 10 minutes UV exposure time, the light transmittance decreased from 90% to 62% and the sheet resistance decreased to 2–3 MΩ/sq.
The oxygen barrier properties of the GO/PEI-deposited film were measured using MOCON. The OTR of the deposited film depended on the number of GO/PEI bi-layers. A bare PET film (188 µm thick) without GO/PEI deposition yielded an OTR of 8.119 cc/m2∙day. The OTR of a deposited film was much lower. As the number of deposition layers increased, the OTR decreased from 8.229 to less than 0.05 cc/m2∙day, the minimum sensitivity of the measurement. The light transmittance of the deposited layer decreased from 99.2% to 89.6% as the number of GO/PEI deposition layers increased. The characteristics of a 3-bilayer deposited film changed as a result of thermal or UV treatment. Deposited films were annealed at 80°C in a convection oven for 1 hour, 80°C in a convection oven for 24 hour, 150°C in a convection oven for 24 hour, and exposed to UV light for 1 hour. The OTR and light transmittance properties differed by film. The film treated at 150°C/24 hours and UV/1 hour, which produced significant amounts of reduced GO, as indicated by the lower light transmittance, yielded an OTR that was higher than that of the film treated at 80°C/1 hour, 80°C/24 hour, which contained less reduced GO. These results indicated the importance of interfacial electric polarity of the deposited film. The less reduced GO included many polar functional groups with negative charges, which induced stronger interfacial bonding with the positively charged PEI in the GO/PEI deposited film.