Capillary replacement between two mutually immiscible liquids on an open channel*

Capillarity-driven microfluidic devices have been receiving considerable attention in engineering and medical applications. Although paper is a well-known material as a capillary pump for pregnancy tests, microgrooves or repetitive microstructure patterns are intensively studied equally well for capillary pumps [1]. Almost all previous capillarity-driven microfluidic devices involve spontaneous flow of a single liquid. Recently, fundamental aspects of the spontaneous replacement between two mutually immiscible liquids have been clarified [2]. However, the physical understanding of the replacement is still premature for microfluidic implementation. In this study, we investigated the capillary replacement on an open channel. In particular, we focused on the spontaneous replacement of a pre-filled aqueous solution with an oil more wettable on the channel surface in an open channel.


[1] A. Olanrewaju et al., Capillary microfluidics in microchannels: from microfluidic networks to capillaric circuits, Lab Chip 18, 2323 (2018).
[2] J. André and K. Okumura, Capillary Replacement in a Tube Prefilled with a Viscous Fluid, Langmuir 36, 10952 (2020).