The spontaneous transport of micro-droplet confined in wetting/non-wetting deformable micro-confinement

Chong-Wai Io^1*, Rau-Sung Liu¹

¹Department of Physics, National Chung-Cheng University, Chia-Yi, Taiwan

* Presenter:Chong-Wai Io, email:phycwio@ccu.edu.tw

The transport of liquid at microscale is always an important topic. Regardless of the active control by applying an external drive (e.g. pressure gradient), the spontaneous transport of micro-droplet under the liquid-boundary interaction has received increasing attention in recent years due to its potential applications for designing smart fluidic devices. Micro-droplet transport induced by wettability gradient, rachet-shaped Leidenfrost substrate, and Marangoni bursting are typical examples. Nevertheless, the transport direction is limited to the wettability, or the droplet properties (volume or concentration) are varied during the transport. Most recently, it is found that once the micro-confinement is deformable and spatially asymmetric, the uni-direction transport for both wetting and non-wetting micro-droplet can be achieved without varying the droplet properties, so-called the bendo-taxis. In this report, we are going to investigate the dynamical evolution of spontaneous transport of a wetting/non-wetting droplet confined in a Hele-Shaw-cell-like deformable micro-confinement with one fixed end and one opened end. Under the micro-capillary adhesion/repulsion force exerted by the micro-droplet, the boundary is deformed and the degree of deformation at the fixed/opened end is smaller/larger, which subsequently induced the asymmetric Laplace pressure to drive the droplet motion. The negative/positive Laplace pressure for the wetting/non-wetting droplet pulls/pushes at the front/rear edge always drive the droplet toward the edge with higher deformability.

Keywords: Laplace pressure, micro channel, spontaneous transport