Real-time observation of dynamic structure of liquid-vapor interface at nanometer resolution in electron irradiated sodium chloride crystals

Amy Ren,Edward Wong,A Paul Alivisatos,David Lu,Matthew R Hauwiller,Gang Ren

doi:10.1038/s41598-020-65274-9

Abstract

The dynamics and structure of the liquid and vapor interface has remained elusive for decades due to the lack of an effective tool for directly visualization beyond micrometer resolution. Here, we designed a simple liquid-cell for encapsulating the liquid state of sodium for transmission electron microscopic (TEM) observation. The real-time dynamic structure of the liquid-vapor interface was imaged and videoed by TEM on the sample of electron irradiated sodium chloride (NaCl) crystals, a well-studied sample with low melting temperature and quantum super-shells of clusters. The nanometer resolution images exhibit the fine structures of the capillary waves, composed of first-time observed three zones of structures and features, i.e. flexible nanoscale fibers, nanoparticles/clusters, and a low-pressure area that sucks the nanoparticles from the liquid to the interface. Although the phenomenons were observed based on irradiated NaCl crystals, the similarities of the phenomenons to predictions suggest our real-time ovserved dynamic structure might be useful in validating long-debated theoretical models of the liquid-vapor interface, and enhancing our knowledge in understanding the non-equilibrium thermodynamics of the liquid-vapor interface to benefit future engineering designs in microfluidics.

Highlights

The dynamics and structure of the liquid and vapor interface has remained elusive for decades due to the lack of an effective tool for directly visualization beyond micrometer resolution
Since Gibbs’ fundamental works on thermodynamics a century ago[1], many models have been proposed to describe the dynamic structure of the interface between liquid and vapor, which is crucial for our understanding of the important processes in microfluidics, microbiology, and cooling systems for microelectronics[2,3]
The fluid was generated by the electron beam irradiated NaCl crystals, which were sandwiched between Formvar plastic films coated on two transmission electron microscopic (TEM) grids (Fig. 1A–F)

Summary

Introduction

The dynamics and structure of the liquid and vapor interface has remained elusive for decades due to the lack of an effective tool for directly visualization beyond micrometer resolution. (i) A zero-width capillary-wave model, which is a thin-layer interface model that was developed by Gibbs based on the fundamental theory of thermodynamics, laterly refined by Buff et al.[4] In this model, the interface is treated as capillary waves created under surface tension excited by Brownian motion. Transmission electron microscopy (TEM) has the capability to image hard materials at atomic resolution, the TEM vacuum column limits the imaging of liquid and vapor samples due to evaporation To overcome this weakness, scientists recently developed a liquid-cell to encapsulate the liquid, sealing the liquid sample within a small and thin chamber[12,13]. The materials often used to observe the chemical reaction and nanoparticle dynamics in liquid include graphene[12] and silicon nitride[13]

Methods

Results

Discussion

Conclusion