Layer-by-layer water filling in molecular-scale capillaries
Mingwei Chen, Jingshan Wang, Artem Mishchenko, Ivan Timokhin, Fengchao Wang + 2 more
TLDR
This paper reveals that water fills molecular-scale capillaries layer-by-layer in flexible pores and abruptly in rigid ones.
Key contributions
- Observed layer-by-layer water filling in flexible nanocapillaries using atomic force microscopy.
- Flexible walls deform in ~3 Å steps, corresponding to sequential entry of individual water layers.
- Rigid capillaries exhibit abrupt water filling, contrasting with the discrete filling in flexible ones.
- Filling regimes are explained by competition between deformation energy and wall-water interactions.
Why it matters
This research highlights how water's molecular discreteness profoundly impacts capillary phenomena at the nanoscale. Understanding wall compliance's role in selecting between discrete and abrupt filling is crucial for various natural and technological applications.
Original Abstract
Under ambient humidity, water spontaneously condenses in pores only a few nanometers in size, making nanoscale capillarity central to numerous natural phenomena and technological applications. At these dimensions, water may no longer be treated as a continuous fluid, yet the consequences of molecular discreteness for capillary condensation and filling remain poorly understood. Here we study nanocapillaries fabricated by van der Waals assembly and, using atomic force microscopy, monitor their wall deformations during humidity-driven water uptake. We observe two distinct regimes: layer-by-layer filling of flexible capillaries and abrupt filling of rigid ones. Flexible walls deform in steps of ~3 Å, corresponding to the sequential entry of individual water molecular layers. The different filling regimes are explained by the competition between deformation energy and oscillatory wall-water interactions. Our findings show that the molecular discreteness of water can profoundly affect ubiquitous capillary phenomena, with wall compliance selecting between discrete and abrupt filling.
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