Inkjet drawing dynamics of conductive polymer droplets on cellulose nanopapers

The processes of wetting and solvent evaporation in the drying sessile conductive ink droplets formed by inkjet printing are clarified for characterization to be referenced for diverse applications. The electric resistance of the PEDOT:PSS ink line patterns on the nanopaper, the film material of cellulose nanofibers, is affected by the shape and structure of the wire, which are dominated by the elementary process of the droplet drying dynamics. The evaporation flow rate of the ink droplets on the nanopapers decreases at the later stage of the drying process. This is dominated by the decrease in the air–liquid interfacial surface area, while the evaporation flux is roughly constant. The wetting of droplets formed by the inkjet printer is different from the quasi-static droplet placement. The contact angles of sufficiently smaller droplets are smaller, indicating higher apparent wettability because of the momentum effect. This is distinguished from the gravity effect. The conductive particles in the ink help the droplet pinning on the substrate. The nanopapers also tend to pin the droplet peripheries compared to the slide glass. Nevertheless, the radii of both water and the conductive ink droplets on the nanopapers first increase and then decrease later. The initial slow increase in the radius is distinguished from the spreading by the inkjet momentum and is likely to be caused by the capillary effect of the fine texture of the nanopapers. This trend is significant for larger droplets, but the colored dry spots of the ink were smaller than the maximum droplet radii during drying.