Dynamics of Drying Process of Polymer Solution Droplets: Analysis of Polymer Transport and Control of Film Profiles

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We report a series of experimental works about the drying process of polymer solution droplets. Our aims are to analyze the local polymer transport in the drying droplet and to precisely control the profile of polymer film formed after the droplet dries up. For the analysis of the polymer transport, we have established a dynamical observation method for the polymer concentration field by combining the fluorescence microscopy with the lateral profile observation. We observed that a large spatial inhomogeneity of the polymer concentration grows inside the droplet which is caused by the outward capillary flow. For the control of the film profile, we proposed two methods: adding the small amount of surfactant and switching between the solvent evaporation and condensation. These two processes enable us to make a polymer film having a flat profile. Our results propose effective suggestions for controlling the fabrication process of polymer films in inkjet-printing technologies.