Droplet Manipulation: Magically Cut Apart Microdroplet by Smart Nanofibrils Wire

Abstract

only via magical action of an ethanolwetted nanofibrils wire (ENW). The ENW can be designed and fabricated via electronspinning and liquid-infused processes. We reveal that ENW can smartly cut the spreading water droplets via manipulation on a surface, without other external energy. We demonstrate that spreading water droplets with volume of 5-25 µL can be accurately cut apart into various proportions (e.g., 1/9-1/1) by manipulating ENW, and the minimum proportion would be 1.7 µL in volume, without loss. Furthermore, we demonstrate that the radial-crossed 3-5 ENWs can cut apart a spreading droplet effectively into split droplets (SDs) pattern in one step. Especially, we demonstrate that the SDs can be manipulated to move to target regions (e.g., microreactors) via actions of ENW. These findings offer insights into design of novel materials that would be used to manipulate the various liquid microdroplets on a superhydrophilic surface, where droplet movement follows guide of magical ENW, without other external energy, which would be extended into microfluidics, microreactors, etc.The magical ENW can be designed by using electrospinning PAN (poly-acrylonitrile) nanofibers surrounding a 100 µm nylon-main fiber, along with a hydrothermal reaction for a hierarchical high-porosity interlaced network and ethanol-infused process (the details are presented in Figure S1, Supporting Information). The ENW is composed of nanofibrils that are covered with nanopetals (Figure 1a, the inset). The nanopetals makes rough nanoporous surface of nanofibrils, which can be a high capillary to improve the wetting (a typical case can be seen in Figure S2, Supporting Information). [25] Accordingly, a magical ENW can be achieved into robustness after ethanol-infused inside nanoporous surface of ENW. Finally, it is expected that ENW can be used to cut apart a spreading microdroplet on a superhydrophilic surface, that is, a spreading microdroplet would be cut apart into split droplets (e.g., SD-1, and SD-2, respectively, Figure 1a) by means of unique vapor-liquid repellency effect. To best of our knowledge, such droplet splitting behavior is not reported so far.It is found that when such an ENW horizontally approaches to the upper of a spreading droplet and achieves the stronger concave of the spreading droplet, and finally cut apart intoThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/admi.202000161.Microdroplet manipulation is significant in some situations, for example, self-organization of materials, [1] droplet transport, [2][3][4][5] droplet rebounding, [6,7] spontaneous droplet trampolining, [8] liquid pattern, [9][10][11] droplet-based sensor, [12] anti-icing, [13] and water harvesting, [14,15] droplet self-division, [16][17][18] droplet controlling in microfluidics, [19][20][21][22] droplet splitting, [23] multi-phase fluid interactions, [24] etc. For manipulating the microdroplet, some external actions (e.g., electronic, [19,20] magnetic, [21] photo, [25] etc.) are usual...

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