Hybrid Self-Assembly during Evaporation Enables Drop-on-Demand Thin Film Devices

We propose and demonstrate a hybrid self-assembly process as the mechanism for producing strikingly uniform deposits from evaporating drops composed of cosolvents. This assembly process leverages both particle-fluid interactions to carry the particles to the drop surface and particle-interface interactions to assemble the particles into a uniform film. We anchor our results in a cosolvent evaporation model that agrees with our experimental observations. We further employ the process to produce thin film devices such as flexible broadband neutral density filters and semitransparent mirrors. Our observations suggest that this assembly process is free of particle-substrate interactions, which indicates that the results should be transferable across a multitude of material/substrate systems.