Micro Nano Bio-Fluidics Unit, Fluid Systems Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
Langmuir. 2020 Jun 2;36(21):5960-5966. doi: 10.1021/acs.langmuir.0c00846. Epub 2020 May 21.
The manipulation of aqueous droplets has a profound significance in biochemical assays. Magnetic field-driven droplet manipulation, offering unique advantages, is consequently gaining attention. However, the phenomenon relating to diamagnetic droplets is not well understood. Here, we report the understanding of trapping and coalescence of flowing diamagnetic aqueous droplets in a paramagnetic (oil-based ferrofluid) medium using negative magnetophoresis. Our study revealed that the trapping phenomenon is underpinned by the interplay of magnetic energy () and frictional (viscous) energy (), in terms of magnetophoretic stability number, = (/). The trapping and nontrapping regimes are characterized based on the peak value of magnetophoretic stability number, , and droplet size, *. The study of coalescence of a trapped droplet with a follower droplet (and a train of droplets) revealed that the film-drainage Reynolds number () representing the coalescence time depends on the magnetic Bond number, . The coalesced droplet continues to remain trapped or gets self-released obeying the and * criterion. Our study offers an understanding of the magnetic manipulation of diamagnetic aqueous droplets that can potentially be used for biochemical assays in microfluidics.
在生化分析中，对水相液滴的操控具有重要意义。磁场驱动的液滴操控具有独特的优势，因此受到了广泛关注。然而，对于抗磁性液滴的相关现象，人们的认识还不够深入。在这里，我们报告了使用负磁泳现象理解在顺磁性（油基铁磁流体）介质中流动的抗磁性水相液滴的捕获和聚结。我们的研究表明，捕获现象是由磁能（ ）和摩擦（粘性）能（ ）共同作用决定的，其特征是磁泳稳定性数 = （ / ）。基于磁泳稳定性数的峰值 和液滴尺寸 ，可以将捕获和非捕获区域进行特征化。对被捕获液滴与跟随液滴（和一连串液滴）的聚结的研究表明，代表聚结时间的膜排流雷诺数（ ）取决于磁邦数 。聚结后的液滴继续被捕获或根据 和 准则自行释放。我们的研究提供了对抗磁性水相液滴的磁操控的理解，这可能在微流控中的生化分析中得到应用。
