Fabrication\nof Spherical Colloidal Supraparticles\nvia Membrane Emulsification

Colloidal supraparticles are micrometer-scale assemblies\nof primary\nparticles. These supraparticles have potential application in photonic\nmaterials, catalysis, gas adsorption, and drug delivery. Thus, the\nsynthesis of colloidal supraparticles with a narrow size distribution\nand high yield has become essential. Here, we demonstrate membrane\nemulsification as a high-throughput approach for fabricating spherical\nsupraparticles with a narrow size distribution and control over particle\nsize and crystallinity. Spherical supraparticles with well-ordered\nsurface structures are synthesized by generating emulsion droplets\nof an aqueous colloidal dispersion in fluorocarbon oil using a Shirasu\nporous glass membrane followed by the consolidation of particles through\nwater removal within the emulsion. We systematically investigate process\nparameters, including the flow rate of the particle dispersion, the\nparticle concentration, and the average pore diameter of the membrane,\non the mean size and size distribution of the supraparticles, revealing\nkey factors governing supraparticle properties and production throughput.\nA comparative evaluation with commonly employed methods highlights\nthe advantage of membrane emulsification, which combines well-defined\ninternal structure and controlled supraparticle sizes with comparably\nhigh yields on the order of tens of grams per day. Importantly, in\ncontrast to widely used droplet-based microfluidics, membrane emulsification\nallows fabrication of supraparticles in nonfluorinated oil. Overall,\nmembrane emulsification offers a simple yet versatile method for fabricating\ncolloidal supraparticles with high quality and yield and may serve\nas a bridge between existing high-precision techniques, such as droplet-based\nmicrofluidics, and high-throughput processes with less control, such\nas spray-drying.