Nanopores lined with hydrophobic groups function as switches for water and all dissolved species, such that transport is allowed only when applying a sufficiently high transmembrane pressure difference or voltage. Here we show a hydrophobic nanopore system whose wetting and ability to transport water and ions is rectified and can be controlled with salt concentration. The nanopore we study contains a junction between a hydrophobic zone and a positively charged hydrophilic zone. The nanopore is closed for transport at low salt concentrations and exhibits finite current only when the concentration reaches a threshold value that is dependent on the pore opening diameter, voltage polarity and magnitude, and type of electrolyte. The smallest nanopore studied here had a 4 nm diameter and did not open for transport in any concentration of KCl or KI examined. A 12 nm nanopore was closed for all KCl solutions but conducted current in KI at concentrations above 100 mM for negative voltages and opened for both voltage polarities at 500 mM KI. Nanopores with a hydrophobic/hydrophilic junction can thus function as diodes, such that one can identify a range of salt concentrations where the pores transport water and ions for only one voltage polarity. Molecular dynamics simulations together with continuum models provided a multiscale explanation of the observed phenomena and linked the salt concentration dependence of wetting with an electrowetting model. Results presented are crucial for designing next-generation chemical and ionic separation devices as well as understanding fundamental properties of hydrophobic interfaces under nanoconfinement.

中文翻译：

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疏水纳米孔的整流和盐浓度依赖性润湿

衬有疏水基团的纳米孔充当水和所有溶解物质的开关，这样只有在施加足够高的跨膜压差或电压时才允许传输。在这里，我们展示了一种疏水性纳米孔系统，其润湿性和传输水和离子的能力得到了纠正，并且可以通过盐浓度进行控制。我们研究的纳米孔包含疏水区和带正电的亲水区之间的连接。纳米孔在低盐浓度下关闭以进行传输，并且仅当浓度达到取决于孔开口直径、电压极性和幅度以及电解质类型的阈值时才表现出有限的电流。此处研究的最小纳米孔具有 4 nm 直径，并且在所检查的任何浓度的 KCl 或 KI 中都不会打开用于运输。对于所有 KCl 溶液，12 nm 纳米孔关闭，但在 KI 中以高于 100 mM 的浓度传导负电压的电流，并在 500 mM KI 的两个电压极性下打开。因此，具有疏水/亲水结的纳米孔可以用作二极管，这样人们就可以识别一系列盐浓度，其中孔仅针对一个电压极性传输水和离子。分子动力学模拟与连续介质模型一起提供了对观察到的现象的多尺度解释，并将润湿的盐浓度依赖性与电润湿模型联系起来。