@article{847b82521bf34a5aa6b6fb412bb2a5a2,
title = "Directional pumping of water and oil microdroplets on slippery surface",
abstract = "Transporting water and oil microdroplets is important for applications ranging from water harvesting to biomedical analysis but remains a great challenge. This is due to the amplified contact angle hysteresis and insufficient driving force in the micrometer scale, especially for low-surface energy oil droplets. Coalescence of neighboring droplets, which releases vast additional surface energy, was often required, but its relatively uncontrollable nature brings uncertainties to the droplet motion, and the methodology is not applicable to single droplets. Here we introduce a strategy based on slippery surface with immobilized lubricant menisci to directionally transport microdroplets. By simply mounting hydrogel dots on slippery surface, the raised menisci remotely pump microdroplets via capillary force with high efficiency, regardless of droplet size or surface energy. By proof-of-concept experiments, we demonstrate that our method allows for highly efficient water droplet collection and highly sensitive biomedical analyte detection.",
keywords = "Antifouling, Capillary force, Droplet transport, Microdroplet, Slippery surface, n/a OA procedure",
author = "Jieke Jiang and Jun Gao and Hengdi Zhang and Wenqing He and Jianqiang Zhang and Dan Daniel and Xi Yao",
note = "Funding Information: 5. Jokinen V, Leinikka M, Franssila S (2009) Microstructured surfaces for directional wetting. Adv Mater 21:4835–4838. Methods Material Fabrication. The 4 wt \% sodium alginate (Sigma-Aldrich) solution was printed onto thermally curable PDMS precursor (Dow Corning Sylgard 184, 10:1 base and curing agent). PDMS precursor was spin-coated on a clean glass slide at a rotating speed of 3,000 rpm by using a spin-coater (KW-4A, Institute of Microelectronics of Chinese Academy of Sciences). A dispensing system (AD1520; Biodot) was applied to print alginate sodium solution on liquid PDMS precursor film. The resulting sample was annealed at 80 °C for 5 h before immersed into a 500 mM CaCl2 solution for 0.5 h for the gelation of hydrogel dots. Then the PDMS film was immersed into silicone oil (10cSt; Sigma-Aldrich) for 5 h to swell the PDMS and form an immobilized lubricant meniscus. To control the thickness of the overcoated layer, the oil on the surface was gently wiped by filter papers, and the same oil with controlled volume was added to a known surface area of the sample. GFP-expressing E. coli was used in the test of bacterial collection and detection. Characterization. Microdroplets were generated by two methods: the spraying method and the single-droplet method. For the spraying method, a thin film chromatography sprayer (250 mL; Sigma Aldrich) was used to generate the microdroplets. The sprayer was placed at about 15 cm distance to the surface and sprayed for one time in a single experiment. Alternatively, microdroplets with controlled diameter were generated individually by a homemade super-hydrophobic needle. The microdroplet movements were recorded by a horizontally placed microscope equipped with a high-speed CCD (i-speed 3; Olympus). 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year = "2019",
month = feb,
day = "12",
doi = "10.1073/pnas.1817172116",
language = "English",
volume = "116",
pages = "2482--2487",
journal = "Proceedings of the National Academy of Sciences of the United States of America",
issn = "0027-8424",
publisher = "National Academy of Sciences",
number = "7",
}
SDG 6 Clean Water and Sanitation