Davanlou Ashkan, Kumar Ranganathan
Mechanical &Aerospace Engineering, University of Central Florida, Orlando, Florida 32816, USA.
Sci Rep. 2015 May 7;5:9531. doi: 10.1038/srep09531.
Micro-total analysis systems (μTAS) have attracted wide attention and are identified as a promising solution for sample transport, filtration, chemical reactions, separation and detection. Despite their popularity, the selection of an appropriate mechanism for droplet transport and coalescence has always been a challenge. This paper investigates the use of Marangoni flow as a mechanism for levitating and transporting droplets on immiscible liquid films at higher speeds than is possible currently. For the first time, we show that it is possible to realize the natural coalescence of droplets through Marangoni effect without any external stimulation, and deliver the coalesced droplet to a certain destination through the use of surface tension gradients. The effects of shape and size on collision outcome are studied. Regions of coalescence and stretching separation of colliding droplets are delineated based on Weber number and impact number. In addition, the effect of viscosity on post collision regimes is studied. The findings in this fundamental study can be beneficial to many applications such as welding, drug delivery and microfluidics devices in controlling small droplets and targeting them to various locations.
微全分析系统（μTAS）已引起广泛关注，并被视为样品传输、过滤、化学反应、分离和检测的一种有前景的解决方案。尽管它们很受欢迎，但选择合适的液滴传输和聚并机制一直是一个挑战。本文研究了利用马兰戈尼流作为一种机制，以比目前更高的速度在不混溶液膜上悬浮和传输液滴。我们首次表明，通过马兰戈尼效应，无需任何外部刺激就有可能实现液滴的自然聚并，并利用表面张力梯度将聚并后的液滴输送到特定目的地。研究了形状和尺寸对碰撞结果的影响。基于韦伯数和冲击数划定了碰撞液滴的聚并和拉伸分离区域。此外，还研究了粘度对碰撞后状态的影响。这项基础研究中的发现可能有益于许多应用，如焊接、药物递送和微流控装置，用于控制小液滴并将它们靶向输送到不同位置。
