Capillary-Assisted Printing of Structured Colloidal Monolayers

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Thin films made of micrometer-sized particles can be used in sensing, optical coatings, anti-counterfeiting, and electronics. These applications require that the position and orientation of each particle in the film be tightly controlled. Contemporary manufacturing techniques are unable to provide this level of precision. This award supports fundamental research to create a new additive manufacturing technique that uses the interface of a liquid droplet (a template) to build ordered particle films. The particles are delivered to the surface of the template, where they assemble under the subtle forces that exist at the interface. The droplet evaporates and the particle assembly is mapped to the underlying substrate, creating a dry ordered thin film. The research team will combine computer simulations and experimental testing to discover the relationship between the processing conditions and the characteristics of the thin film deposits. The new knowledge will lead to a scalable platform to manufacture thin film materials with complex patterns from particle building blocks. The educational component of this grant will motivate and train a competitive workforce in advanced manufacturing by focusing on student research experiences and public outreach. A course-based summer program and community activities will be developed to engage students at different levels and the general public. This award will break new ground in engineering thin film materials and contribute to U.S. global leadership in advanced manufacturing.The goal of this project is to create an additive technique for manufacturing dry colloidal monolayers with hierarchical microstructures by exploiting the unique capabilities of interfacial capillary assembly and electrospray targeting. The new method will use a geometrically controlled droplet as a template to assemble two-dimensional crystalline superstructures of microparticles delivered directly to the droplet surface by electrospray. A dry monolayer will be transferred to the underlying structure upon the evaporation of the droplet template. To realize the full application potential of this technique, this research will fill the knowledge gap on the complex interplay of capillary assembly and evaporation-induced transport on non-uniformly curved interfaces. The research team will create surface-evolving models and lattice Boltzmann simulations to predict the interface evolution, droplet hydrodynamics, and particle transport. Advanced flow imaging and particle tracking methods will be applied to validate the model and uncover the underlying physics of structure formation. Electrospray targeting and evaporation experiments will be conducted to test the hypothesis that a surface flow aligned with capillary migration is required to form a structured monolayer in a dry form.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.