Hydrogel Film Assembly Process at Droplet Interface with Evaporation Temperature

Abstract

and its change of properties by various experimental conditions are essential to explain the assembly process.Nanoparticles assembly process and behaviors inside the drying droplet were highly affected by the role of internal flow. Deegan et al. reported the coffeering effect that particles assembled by capillary and Marangoni flow inside the drying droplet. [13] Self-assembled structures like the coffee-ring structure using evaporation could be applied to various research and industrial areas, such as transparent electrodes [14,15] and printing technologies. [16] To control the particles, it is an important issue that understand and physics of Marangoni flow. Therefore, there were different parametric researches to control the Marangoni flow with controlling temperature, [16,17] droplet size, [18] particle size, [19] and shape. [20] These internal flows did not only make the internal assemblies but also make the interfacial assemblies of particles. Im et al. have reported the self-ordered structure of nanoparticles was made from the strong convective flow. [21] Film assembly at the interface was highly affected by internal flow and its characteristics. However, there were more studies needed to apply to functional materials and polymer films assembly.In this research, we investigated the hydrogel assembly to interface film affect by internal flow change with evaporation temperature using a gelatin solution. Changing the evaporation temperature, the morphology of assembled final hydrogel films after droplet evaporation was measured using a profiler and scanning electron microscopy (SEM). Also, its mechanical properties were measured using nanoindenter. From the increasing internal flow, film assembly was enhanced and morphology changed. And film hardness was increased with faster evaporation. We analyze its change in characteristic and visualization of its nanostructures. Results and Discussion Film Morphology Change with Evaporation TemperatureTo evaluate the hydrogel film assembly changing with evaporation temperature, we observed the final film morphology with the temperature change. Figure 1a shows the final film Recently, thin-film assembly at the liquid-air interface has been widely studied. These film scaffolds have high potential to control the crystallization process and fabricate single crystals. However, there have been limitations in understanding and controlling the behavior of polymer chains form into films. This study investigates thin-film assembly at the hydrogel droplet interface with internal flow and its role. During the hydrogel film formation, the internal flow of the droplet is visualized using micro-particle image velocimetry technique at various temperatures. From the droplet evaporation, convection flow induced by heat cause buoyancy effect and pressure on the interface film from evaporation flux affect the film morphology and its mechanical characteristics. Therefore, more dense assembled film is generated on the droplet interface. It is expected that the investigations could give bette...

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