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Controlled assembly of jammed colloidal shells on fluid droplets

Abstract

Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional microcrystalline materials useful in fields as diverse as biomedicine1, materials science2, mineral flotation3 and food processing4. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials used5,6,7,8,9. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.

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Figure 1: Hydrodynamic focusing for the continuous formation of droplets with colloidal armour.
Figure 2: Time-lapse sequence of the capture of an individual particle (indicated with a black arrow).
Figure 3: Packing on the jammed shell.
Figure 4: Various shell–core combinations.
Figure 5: Tailored production of Janus armour.

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Acknowledgements

We thank R. Larsen, A. Lips, L. Mahadevan and R. Subramanian for helpful conversations. Support from Unilever Research and the Harvard Material Research Science and Engineering Center (DMR-0213805) are gratefully acknowledged.

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Correspondence to Howard A. Stone.

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Subramaniam, A., Abkarian, M. & Stone, H. Controlled assembly of jammed colloidal shells on fluid droplets. Nature Mater 4, 553–556 (2005). https://doi.org/10.1038/nmat1412

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