Graphical Abstract

Industrial applications of cellulose nanofibres (CNFs) include the additive to a wide range of materials from display and cosmetic to pigment inks. Many of these expected applications are based on the mixture of colloidal particles and CNFs in aqueous dispersion. In particular, the mixed dispersion is typically processed in such a way that the droplet or shallow wide volume of dispersion is dried on the substrate or container. In this work, the basic physical properties that these diverse kinds of potential applications share in common are focused on. The colloidal films were fabricated consisting of polystyrene particles and CNFs under the condition of various concentration combinations through the drying of aqueous dispersion in polystyrene well plates. It has been found that the films fabricated from higher concentrations of CNF tend to peel-off spontaneously in the drying process. The basic mechanism of phenomenon is attributed to the contraction of CNFs during the drying by hydrogen bonding between the filaments.

Promising versatile applications of cellulose nanofibres (CNFs) include film structures for device substrates and surface coatings. Although there are various factors that affect the textures of such 'nanopapers', the drying from aqueous dispersion of CNF is the typical process to fabricate them. The basic property on this drying process is focused on, paying attention to the influence of temperature on the macroscopic uniformity. On the one hand, higher drying temperature is advantageous for the fast fabrication. On the other hand, too high temperature leads to significant nonuniformity, are focused on of the film. They propose that this drawback is suppressed by the multi-step coating process. The multi-step coating technique is simple without extra introduction of apparatus or chemical species. Therefore, it is a good option, e.g. when trying to fabricate relatively thin film structures where coffee-ring-like phenomena tend to take place.

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.

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