Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process.
Nanoscopic characterization of the water vapor-salt interfacial layer reveals a unique biphasic adsorption process.
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水蒸气-盐界面层的纳米表征揭示了独特的双相吸附过程
DOI：
10.1038/srep31688
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发表时间：
2016-08-16
影响因子：
4.6
通讯作者：
Shao Z
中科院分区：
文献类型：
--
作者：
Yang L;He J;Shen Y;Li X;Sun J;Czajkowsky DM;Shao Z
我们的定量了解水吸附到盐表面在环境条件下是目前相当差，由于在这些条件下直接表征这一界面层的困难。在这里，我们确定在不同的相对湿度（RH）的基础上的一种新的应用原子力光谱和毛细管凝聚理论的界面层在NaCl上的厚度。特别是，我们利用毛细凝聚过程的微秒时间尺度直接解决其贡献的大小在针尖样品相互作用，从该界面水厚度的确定。此外，为了将该厚度与盐溶解相关联，我们还在类似条件下测量表面电导。我们发现，低于30%RH，基本上只有水分子沉积到这个表面上，典型的常规吸附到固体表面上。然而，高于30%RH，吸附与离子的溶解是同时的，不同于常规吸附，导致表面电导的快速增加。因此，水在NaCl上的吸附是一种非常规的两相过程，其中界面层不仅表现出厚度上的定量差异，而且还表现出组成上的定性差异。
Our quantitative understanding of water adsorption onto salt surfaces under ambient conditions is presently quite poor owing to the difficulties in directly characterizing this interfacial layer under these conditions. Here we determine the thickness of the interfacial layer on NaCl at different relative humidities (RH) based on a novel application of atomic force spectroscopy and capillary condensation theory. In particular, we take advantage of the microsecond-timescale of the capillary condensation process to directly resolve the magnitude of its contribution in the tip-sample interaction, from which the interfacial water thickness is determined. Further, to correlate this thickness with salt dissolution, we also measure surface conductance under similar conditions. We find that below 30% RH, there is essentially only the deposition of water molecules onto this surface, typical of conventional adsorption onto solid surfaces. However, above 30% RH, adsorption is simultaneous with the dissolution of ions, unlike conventional adsorption, leading to a rapid increase of surface conductance. Thus, water adsorption on NaCl is an unconventional biphasic process in which the interfacial layer not only exhibits quantitative differences in thickness but also qualitative differences in composition.