Electric Field and Ion Diffusion Triggered Precisely Regulated Construction of Micron-scale Water-based Polymer Films: a Detailed Mechanistic Exploration

Water-based polymer films can be readily deposited onto a wide range of metallic materials as an environmentally friendly coating through the demulsification-induced fast solidification(DIFS) method. However, there is still a lack of in-depth understanding of the demulsification process of the water-based emulsions and their deposition processes. Herein, we demonstrate that the build-up process of the commercial water-based micron-scale waterborne polyurethane, polyvinyl acetate, polyurethane acrylate, and natural rubber polymer films is affected by the collective effect of electric field and ion diffusion exerted by anode-cathode electrode pairs, applied voltage, conduction time, electrode distance, and emulsion species. A structural investigation of as-prepared polymer films allows us to propose two new structure build-up models. During a flat film deposition, isolated islands are formed first and grow on the substrate surface, and eventually, their mutual coalescence forms the final layer. Whereas, for a convex layer formation, the layer is first formed in the middle of the substrate and then grows toward the sides of the convex structure of the substrate. The results presented in this work expand the understanding of the mechanism of the DIFS process and may provide some new insights into structure-oriented multifunctional material design.