Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids
Gradient Quasi‐Liquid Surface Enabled Self‐Propulsion of Highly Wetting Liquids
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DOI：
10.1002/adfm.202008614
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发表时间：
2021-01
影响因子：
19
通讯作者：
Lei Zhang;Zongqi Guo;Jyotirmoyee Sarma;Weiwei Zhao;X. Dai
中科院分区：
文献类型：
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作者：
Lei Zhang;Zongqi Guo;Jyotirmoyee Sarma;Weiwei Zhao;X. Dai
高润湿性液体的自推进在热交换器、空调和制冷系统中非常重要。然而，实现这种自发运动是具有挑战性的，因为这些液体由于其超低的表面张力而倾向于润湿所有表面。尽管广泛的非对称表面结构和梯度化学涂层被开发用于定向液滴传输，但它们将被这些液体淹没和覆盖。在这里，这一挑战通过创建梯度准液体表面来解决，以实现表面张力低至10.0 mN m−1的液滴自推进。通过用梯度接枝密度系留柔性聚合物而设计的这种表面显示出对高度润湿液体的超低接触角滞后（<1 °）。因此，该表面可以同时通过梯度润湿性提供足够的驱动力和通过用于自发液滴运动的滑动边界润滑提供可忽略的保持力。此外，通过在模拟冷凝条件下喷射高度润湿的液体实现了微小液滴的连续自推进，并证明了增加温度梯度可以进一步加速自推进。这项研究提供了一个新的范例，以促进被动去除高度润湿的液滴，导致在增强冷凝传热的潜在影响，无论表面取向。
Self‐propulsion of highly wetting liquids is important in heat exchanger, air conditioning, and refrigeration systems. However, it is challenging to achieve such a spontaneous motion as these liquids tend to wet all the surfaces due to their ultralow surface tensions. Despite that extensive asymmetric surface structures and gradient chemical coatings are developed for directional droplet transport, they will be flooded and covered by these liquids. Here, this challenge is addressed by creating a gradient quasi‐liquid surface to achieve the self‐propulsion of droplets with surface tensions down to 10.0 mN m−1. Such a surface engineered by tethering flexible polymers with gradient grafting density shows ultralow contact angle hysteresis (<1o) to highly wetting liquids. Thus, the surface can simultaneously provide sufficient driving forces through the gradient wettability and negligible retention forces through the slippery boundary lubrication for spontaneous droplet movement. Moreover, continual self‐propulsion of tiny droplets is achieved by spraying highly wetting liquids in simulated condensation conditions and demonstrates that adding temperature gradient can further accelerate the self‐propulsion. The study provides a new paradigm to promote passive removal of highly wetting droplets, leading to potential impacts in enhancing condensation heat transfer regardless of surface orientations.