Sanders Kate A, De Volder Michael F L
Department of Engineering, University of Cambridge, 17 Charles Babbage Road, Cambridge CB3 0FS, U.K.
Langmuir. 2025 Aug 19;41(32):21780-21789. doi: 10.1021/acs.langmuir.5c02866. Epub 2025 Aug 6.
Microscale emulsion droplets are versatile soft templates for assembling nanoparticle powders and forming secondary microparticles. When combined with microfluidics, nanostructured microparticles can be produced with precise size and uniformity. However, assembly requires removal of the droplet solvent, which is particularly slow for water-in-oil emulsions. This has been a longstanding challenge, preventing the deployment of emulsion-structured nanomaterials at scale. Here, an osmotic pressure-driven method is presented that achieves controlled water extraction from emulsion droplets. This is a faster, more cost-effective, and sustainable alternative to prolonged heating; particle solidification is achieved by introducing a second emulsion containing a high solute concentration. The effect of system composition and droplet size on the rate of water extraction, emulsion stability, and nanoparticle assembly is explored, generating an empirical model for the solidification of 100-1000 μm diameter template droplets. By combining this extraction method with microfluidic emulsification, batches of spherical microparticles were formed composed entirely of nanoparticles, in this case, carbon nanotubes as a model system. Particle solidification was up to 5 times faster than evaporation while maintaining control over morphology and size distribution. Additionally, this processing method was demonstrated on other nanoparticle systems, confirming a broad material applicability.
微尺度乳液滴是用于组装纳米颗粒粉末和形成次级微粒的通用软模板。当与微流体技术结合时，可以生产出具有精确尺寸和均匀性的纳米结构微粒。然而，组装需要去除液滴溶剂，对于油包水乳液来说，这一过程特别缓慢。这一直是一个长期存在的挑战，阻碍了乳液结构纳米材料的大规模应用。在此，提出了一种渗透压驱动的方法，该方法可实现从乳液滴中可控地提取水分。这是一种比长时间加热更快、更具成本效益且更可持续的替代方法；通过引入含有高溶质浓度的第二种乳液来实现颗粒固化。研究了系统组成和液滴尺寸对水提取速率、乳液稳定性和纳米颗粒组装的影响，生成了一个关于直径为100 - 1000μm的模板液滴固化的经验模型。通过将这种提取方法与微流体乳化相结合，形成了完全由纳米颗粒组成的球形微粒批次，在这种情况下，以碳纳米管作为模型系统。颗粒固化速度比蒸发快5倍，同时保持对形态和尺寸分布的控制。此外，这种加工方法在其他纳米颗粒系统上也得到了验证，证实了其广泛的材料适用性。
