Hiroyuki Kai

Open microfluidic channels, which capture and transport liquid on flat substrate surfaces through wettability contrast, offer a promising platform for the analysis, mixing, separation, etc. of small‐volume liquid samples. This study focuses on the development of open microfluidic channels featuring oleophilic/oleophobic micropatterning in a hyperbranched, space‐filling structure, thereby creating high‐density channels. These newly designed channels allow for the swift collection of microdroplets with low surface tension within less than 10 s through hierarchical transport and merging of the microdroplets within the channel. The collection efficiency reaches 66% in the channel with the optimized channel geometry. These results underscore the effectiveness of this method for the collection of low surface tension microdroplets, paving the way for the advancement in the domain of open microfluidics of oil, a field that has yet to be fully explored.