One-way wicking in open micro-channels controlled by channel topography

[Display omitted] •Experimentally demonstrated one-way wicking in open microfluid channels.•Tilted fin-like structures are used to generate directional surface-tension effect.•Underlying mechanism is explained qualitatively with a simplified 2D model.•Effects of contact angle, evaporation, and geometry are studied.•A set of general guidelines is established for the design of wicking channels. One-way wicking (microfluidic diode) behaviors of a range of IPA–water mixtures on internally structured PDMS-based open micro-channels were experimentally demonstrated and quantified. The open microfluidic channels, each internally decorated with an array of angled fin-like-structure pairs, were fabricated using a combined photolithography and soft molding procedure. Propagations of wetting fluids were found to be much more impeded on the fin-tilting direction, or the hard wicking direction, comparing to the opposite direction, or the easy wicking direction. This asymmetric wicking behaviors were attributed to the structure-induced direction-dependent Laplace pressure. Two key parameters – the contact angle of the wicking fluid and the tilting angle of the fin-like structures – were studied. The effects of preferential evaporation and wetting instability were also investigated. The findings of this study are expected to provide a better understanding of how fluids interact with micro-scaled structures and to offer a new way of manipulating fluids at the micron and nanometer scales.