Department of Mechanical and Industrial Engineering, University of Massachusetts, 160 Governors Drive, Amherst, Massachusetts 01003, United States.
Langmuir. 2011 Aug 16;27(16):9760-8. doi: 10.1021/la201523r. Epub 2011 Jul 22.
Using a microfluidic flow-focusing device, monodisperse water droplets in oil were generated and their interface populated by either 1 μm or 500 nm amine modified silica particles suspended in the water phase. The deformation and breakup of these Pickering droplets were studied in both pure extensional flow and combined extensional and shear flow at various capillary numbers using a microfluidic hyperbolic contraction. The shear resulted from droplet confinement and increased with droplet size and position along the hyperbolic contraction. Droplet deformation was found to increase with increasing confinement and capillary number. At low confinements and low capillary numbers, the droplet deformation followed the predictions of theory. For fully confined droplets, where the interface was populated by 1 μm silica particles, the droplet deformation increased precipitously and two tails were observed to form at the rear of the droplet. These tails were similar to those seen for surfactant covered droplets. At a critical capillary number, daughter droplets were observed to stream from these tails. Due to the elasticity of the particle-laden interface, these drops did not return to a spherical shape, but were observed to buckle. Although increases in droplet deformation were observed, no tail streaming occurred for the 500 nm silica particle covered droplets over the range of capillary numbers studied.
使用微流控流聚焦装置，生成单分散油包水乳液，并用悬浮在水相中的 1μm 或 500nm 胺改性硅颗粒填充其界面。在各种毛细数下，使用微流道双曲收缩，研究了这些 Pickering 液滴在纯拉伸流和拉伸与剪切组合流中的变形和破裂。剪切由液滴限制产生，并随液滴尺寸和在双曲收缩中的位置而增加。发现液滴变形随限制和毛细数的增加而增加。在低限制和低毛细数下，液滴变形符合理论预测。对于完全受限的液滴，其界面填充有 1μm 的硅颗粒，液滴变形急剧增加，并在液滴后部观察到形成两个尾巴。这些尾巴类似于表面活性剂覆盖液滴的尾巴。在临界毛细数下，观察到从这些尾巴中流出子液滴。由于颗粒负载界面的弹性，这些液滴不会恢复到球形，而是观察到褶皱。尽管液滴变形有所增加，但在研究的毛细数范围内，500nm 硅颗粒覆盖的液滴没有发生尾部流。
