Self-Assembly of Nanoparticles from Evaporating Drops and Liquid Films: Science, Engineering and Applications

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Have you ever wondered at the variety of self assembled deposit structures that can be obtained by evaporating liquids containing nanoparticles on top of a solid substrate. Deposit shapes vary from rings around a coffee drop, to hexagonal cells and fractal patterns. An interdisciplinary team of Columbia University scientists will study the related fascinating multiscale physics, using a combination of experimental, theoretical and numerical techniques. The team has the following skills: multiphase flow (Attinger, PI), colloids (Somasundaran), pattern recognition (Chang) and open-source computational fluid dynamics (Spiegelman). The complex self-assembly of nanoparticles will be studied by using first physical principles to explain the resulting selfassembled patterns (what we call a top-down approach), and by identifying features in the patterns that are signs of specific basic laws or transport rules (bottom-up approach).Intellectual Merit:Experiments will involve the spotting of microdrops of complex fluids on various substrates, fluorescence microscopy and laser profilometry to scan the three dimensional deposits. The first intellectual merit will be to describe with a phase diagram the self-assembly of nanoparticles during liquid evaporation on a solid substrate. The use of a phase diagram in that context is novel and allows a simple but powerful comparison of the magnitude of competing transport phenomena, such as evaporation at the wetting line, Marangoni recirculation, electrostatic and van der Waals forces, buoyancy, and dielectrophoresis. The phase diagram will provide an insight and an overview of the complex interplay between multiphase processes, influenced by the geometry of the liquid drop or film: fluid mechanics, heat transfer, mass transfer, colloidal interactions. Second, an available proprietary 2D-axisymmetric numerical code with a moving mesh able to very accurately track the free surface will be extended to 3D (see Chandra collaboration letter). This will allow the simulation of a wider ranges of boundary conditions, permitting the consideration of thin films and complex geometries. Explaining the self-assembly of nanoparticles from evaporating drops and liquid films from first principles is a challenging approach, given the multiple transport phenomena and time/length scales. Therefore, we will also develop a bottom-up approach based on pattern recognition of selfassembled features. We will test the hypothesis that the patterns tell us the about the physics that created them.Broader Impact:The proposed research will deliver innovative solutions to pattern nanoparticles on solid substrates, with applications in organic electronics and patterning of biomolecules for biosensors. Methods to increase printing resolution by two orders of magnitude (see Sonoplot letter), and to pattern uniform layers of particles will be investigated. The pattern recognition algorithms developed in this proposal will be tested to identify biomolecules (see Zenhausern letter) and enhance the accuracy of bloodstain pattern analysis, in collaboration with forensics expert MacDonell (see collaboration letter). Also, the 3D code developed in this proposal will be distributed freely as an open-source code, allowing every interested scientist to study problems involving drop and film transport phenomena such as drop impact, drop evaporation, film drying. Funding will support one graduate student.