Molecular Diffusion of Ions in Nanoscale Confinement
Molecular Diffusion of Ions in Nanoscale Confinement
复制标题
纳米级限制中离子的分子扩散
DOI：
10.1021/acs.langmuir.2c00248
复制
发表时间：
2022
期刊：
影响因子：
3.9
通讯作者：
Ducker, W. A
中科院分区：
文献类型：
--
作者：
Zhang, Z.;Ducker, W. A
我们测量了阴离子荧光素的扩散，限制在两个玻璃壁之间的纳米级（10-100 nm）水膜中。两块玻璃墙的角度非常轻微，形成了一条裂缝。在带电荧光素扩散到裂纹中之前，荧光素的扩散受到薄膜中存在的惰性电解质 NaCl 的强烈影响。没有惰性电解质时荧光素达到平衡分布的时间比存在电解质时长 10 倍。因此，在离子快速扩散很重要的应用中，建议不要用纯水预润湿密闭空间。我们将这种现象归因于围墙电势的影响。薄膜中未经屏蔽的表面电势严重阻碍了荧光素离子的扩散。随着盐扩散到薄膜中，静电双层的厚度缩小，离子的进一步扩散受到的阻碍较小。另一方面，只要薄膜内的表面电势最初被薄膜内低浓度的电解质屏蔽，离子扩散到薄膜中仅受溶液德拜长度的微弱影响。不同德拜长度的浓度分布随时间的演变与用有限差分法 (FDM) 开发的扩散模型相匹配。
We measured the diffusion of an anion, fluorescein, confined to a nanoscale (10–100 nm) aqueous film between two glass walls. The two glass walls were very slightly angled to form a crack. The diffusion of fluorescein was strongly influenced by the presence of an inert electrolyte, NaCl, in the film prior to the diffusion of charged fluorescein into the crack. The time to reach an equilibrium distribution of fluorescein was 10 times longer without the inert electrolyte than when the electrolyte was present. In applications where rapid diffusion of ions is important, it would therefore be advisable to not prewet a confined space with pure water. We attribute this phenomenon to the effect of the electrical potential of the confining walls. Unscreened surface potential in a thin film severely hinders the diffusion of the fluorescein ion. As salt diffuses into the thin film, the electrostatic double layer shrinks in thickness and further diffusion of ions is less hindered. On the other hand, diffusion of ions into the film is only weakly affected by the Debye length of the solution, provided that the surface potential inside a thin film is initially screened by even a low concentration of electrolyte inside the film. The time evolution of the concentration profile for different Debye lengths matches a diffusion model developed with the finite difference method (FDM).