周鹏,胡建华,李蓓.仿生表面结构设计对液滴冷凝及收集行为的影响[J].表面技术,2023,52(8):355-362, 379.
ZHOU Peng,HU Jian-hua,LI Bei.Effect of Bio-inspired Surface Structure Design on Droplet Condensation and Harvesting Behavior[J].Surface Technology,2023,52(8):355-362, 379 |
| 仿生表面结构设计对液滴冷凝及收集行为的影响 |
| Effect of Bio-inspired Surface Structure Design on Droplet Condensation and Harvesting Behavior |
| 投稿时间：2022-07-22 修订日期：2022-11-22 |
| DOI：10.16490/j.cnki.issn.1001-3660.2023.08.030 |
| 中文关键词: 仿生表面 纳米阵列 亲疏水比 楔形顶角 冷凝 定向运动 分子动力学模拟 |
| 英文关键词:bio-inspired surface nanoarray hybrid wettability ratio wedge angle condensation directional motion molecular dynamics simulation |
| 基金项目:华中科技大学材料成形与模具技术国家重点实验室开放课题研究基金(P2021-009) |
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| Author | Institution |
| ZHOU Peng | School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China |
| HU Jian-hua | School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China |
| LI Bei | School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China;State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology, Wuhan 430070, China |
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| 中文摘要: |
| 目的 提高仿生表面液滴冷凝及收集效率。方法 借鉴典型生物微纳结构及表面特性，采用分子动力学方法，建立水汽冷凝演化模型，分析纳米阵列形貌、亲疏水比及楔形顶角对液滴冷凝及收集行为的影响。结果 液滴在方形阵列结构中易钉扎，不利于去除;在矩形阵列结构中具有较好的流动性，且相对方形阵列表面凝结量提升了30.8%。随着亲疏水比θ的增加，沉积在阵列间隙的水分子数增多，钉扎效应加剧，更易形成膜状冷凝;相反地，θ越小，液滴倾向形成滴状冷凝并呈现Cassie态。调整楔形阵列的顶角α可以有效实现液滴的定向运动。当α为3°或6°时，楔形结构能够产生足够的Laplace压力差，驱使液滴定向运动;当α为9°或12°时，能够引导液滴在楔形结构尾端聚集，并融合成更大尺寸的液滴，凝结量相对α为0°分别提升了210.7%和193.0%，收集效率显著提高。相比于单一的仿生表面，结合沙漠甲虫和仙人掌的耦合集水策略设计出的双重仿生结构在凝结量及最大液滴尺寸上均有明显提升，有效提高了液滴的冷凝及收集效率。结论 通过调节纳米阵列形貌和楔形顶角，并合理设置亲疏水比，可有效提高液滴冷凝及收集效率。研究结果为强化冷凝功能的仿生表面设计提供了一定的理论指导。 |
| 英文摘要: |
| Bio-inspired water harvesting surfaces present superb self-cleaning and self-propelling properties, high efficiency, and low energy consumption, and are thus of remarkably importance in numerous industrial applications, including dew formation, power generation, seawater desalination and thermal management, etc. Inspired by nature, i.e., desert beetles and cactuses, these surfaces generally involve micro/nanostructures with unique wettability and shapes that make use of alternating hydrophilic and hydrophobic regions and/or conical shape induced wettability gradients. However, a complete and direct picture for underlying principles and mechanisms of droplet condensation and harvesting on the bio-inspired surfaces at small scales is still an imperative requirement. For this, molecular dynamics (MD) simulation is a powerful tool to investigate liquid thermodynamics from an atomic/molecular perspective. Therefore, in this work, we utilized MD simulations to study water vapor condensation and harvesting behavior on the bio-inspired surfaces. The water vapor condensation model coupled with unique micro/nanostructures and surface wettability was constructed. The effects of surface morphology, hybrid wettability ratio (θ) and wedge angle (α)on droplet condensation and harvesting were then systematically investigated. By constructing hydrophobic square and rectangular nanoarrays on solid substrates, the effect of the surface morphologies on droplet condensation behavior was at first explored. It was shown that the water droplet was prone to get pinned in the square nanostructures and hard to be shed from the surfaces; while the rectangular nanorods offered more supports for the droplet, thereby improving its mobility and effectively alleviating the pinning effect. The total condensed water molecules on the surface with rectangular nanorods were also observed to be increased by 30.8% as compared to those on the surface with square nanostructures. Moreover, either dropwise or filmwise condensation typically occurred on a cold surface depending on the surface wettability. It was thus significantly important to design a stable and controllable surface that was capable of dropwise condensation. To achieve it, a reasonable surface chemistry or hybrid wettability ratio θ should be designed apart from the unique nanostructures. It was found that, as the θ increased, the pinning effect became more severe and the stuck water molecules presented the filmwise condensation mode, which impeded the droplet flow and deteriorated the harvesting performance. Conversely, the droplet could follow the dropwise condensation mode at a smaller θ (i.e., 1/6 and 2/6), which promoted droplet mobility and collection with a Cassie state. In addition, a wedge-shaped structure was beneficial for droplet repellency and directional transportation. Therefore, by combining the hybrid wettability and wedge-shaped nanostructure, the effect of the wedge angle α on the droplet condensation and harvesting was examined. The results showed that, the wedged nanostructure could produce sufficient Laplace pressure difference to drive the directional motion towards to the end of the wedges at α=3° or 6°; while the droplets were found to aggregate and merge into larger droplets directly at the end of the wedges at α=9° or 12°, due to the decreasing surface areas at the front of the wedges. As compared with the rectangular nanostructure (i.e., α=0°), the amount of the condensed water molecules was improved by 210.7% and 193.0% at α=9° or 12°, respectively. More importantly, the dual bionic surface inspired from the desert beetles (i.e., hybrid wettability) and cactuses (i.e., wedge-shaped structures) exhibited excellent water condensation and harvesting performance, in terms of the condensation quantity and the largest droplet size, thereby signifying the feasibility and superiority of dual or multiple bionic surfaces over single bionic or hydrophobic ones. The findings in this work are thus believed to provide the atomic/molecular understanding of water droplet condensation and harvesting behaviors on bio-inspired surfaces. |
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