期刊
PHYSICAL REVIEW X
卷 7, 期 2, 页码 -出版社
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevX.7.021036
关键词
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资金
- Hong Kong RGC [GRF 14303415, CRF C6004-14G]
- Hong Kong RGC (CUHK Direct Grants) [3132743, 3132744, 4053167]
- Hong Kong RGC (CUHK United College Lee Hysan Foundation Research Grant)
- Hong Kong RGC (Endowment Fund Research Grant Schemes)
When a droplet gently lands on an atomically smooth substrate, it will most likely contact the underlying surface in about 0.1 s. However, theoretical estimation from fluid mechanics predicts a contact time of 10-100 s. What causes this large discrepancy, and how does nature speed up contact by 2 orders of magnitude? To probe this fundamental question, we prepare atomically smooth substrates by either coating a liquid film on glass or using a freshly cleaved mica surface, and visualize the droplet contact dynamics with 30-nm resolution. Interestingly, we discover two distinct speed-up approaches: (1) droplet skidding due to even minute perturbations breaks rotational symmetry and produces early contact at the thinnest gap location, and (2) for the unperturbed situation with rotational symmetry, a previously unnoticed boundary flow around only 0.1 mm/s expedites air drainage by over 1 order of magnitude. Together, these two mechanisms universally explain general contact phenomena on smooth substrates. The fundamental discoveries shed new light on contact and drainage research.
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