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Droplet impacts on solid surfaces produce a wide variety of phenomena such as spreading, splashing, jetting, receding, and rebounding. In microholed surfaces, downward jets through the hole can be caused by the high impact inertia during the spreading phase of the droplet over the substrate as well as the cavity collapse during recoil phase of the droplet. We investigate the dynamics of the jet formed through the single hole during the impacting phase of the droplet on a micro-holed hydrophilic substrate. The sub-millimeter circular holes are created on the 0.2 mm-thickness hydrophilic plastic films using a 0.5 mm punch. Great care has been taken to ensure that the millimeter-sized droplets of water dispensed by a syringe pump through a micropipette tip can impact directly over the micro-holes. A high-speed video photography camera is employed to capture the full event of impacting and jetting. A MATLAB code has been developed to process the captured videos for data analysis. We study the effect of impact velocity on the jet formation including jet velocity, ejected droplet volume, and breakup process. We find that the Weber number significantly affects outcomes of the drop impact and jetting mechanism. We also examine the dynamic contact angle of the contact line during the spreading and the receding phase.
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Gradient Droplet Arrays by Acceleration‐Mode Dip‐Coating
Abstract Droplet microarray technology is of great interest in biology and chemistry as it allows for significant reactant savings and massive parallelization of experiments. Upon scaling down the footprint of each droplet in an array, it becomes increasingly challenging to produce the array drop‐by‐drop. Therefore, techniques for parallelized droplet production are developed, e.g., dip‐coating of biphilic substrates. However, it is in general difficult to tailor the characteristics of individual droplets, such as size and content, without updating the substrate. Here, the method of dip‐coating of uniformly patterned biphilic substrates in so‐called “acceleration‐mode” to produce droplet arrays featuring gradients in droplet height for fixed droplet footprint is developed. The results herein present this method applied to produce drops with base diameters varying over orders of magnitude, from as high as 6 mm to as small as 50 µm; importantly, the experimentally measured power‐law‐dependency of volume on capillary‐number matches analytical theory for droplet formation on heterogenous substrates though the precise quantitative values likely differ due to 2D substrate patterning. Gradient characteristics, including average droplet volume, steepness of the gradient, and its monotonicity, can all be tuned by changing the dip‐coating parameters, thus providing a robust method for high‐throughput screening applications and experiments.
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- Award ID(s):
- 2011754
- PAR ID:
- 10500033
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 9
- Issue:
- 22
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/admi.202200667
