In order to permeate a nanopore, an ion must overcome a dehydration energy barrier caused by the redistribution of surrounding water molecules. The redistribution is inhomogeneous, anisotropic and strongly position-dependent, resulting in complex patterns that are routinely observed in molecular dynamics simulations. Here, we study the physical origin of these patterns and of how they can be predicted and controlled. We introduce an analytic model able to predict the patterns in a graphene nanopore in terms of experimentally accessible radial distribution functions, giving results that agree well with molecular dynamics simulations. The patterns are attributable to a complex interplay of ionic hydration shells with water layers adjacent to the graphene membrane and with the hydration cloud of the nanopore rim atoms, and we discuss ways of controlling them. Our findings pave the way to designing required transport properties into nanoionic devices by optimising the structure of the hydration patterns.

为了渗透纳米孔，离子必须克服由周围水分子重新分布引起的脱水能垒。重新分布是不均匀的、各向异性的并且强烈依赖于位置，导致在分子动力学模拟中经常观察到的复杂模式。在这里，我们研究这些模式的物理起源以及如何预测和控制它们。我们引入了一种分析模型，该模型能够根据实验上可访问的径向分布函数预测石墨烯纳米孔中的图案，给出的结果与分子动力学模拟非常吻合。这些图案归因于离子水合壳与石墨烯膜附近的水层以及纳米孔边缘原子的水合云之间的复杂相互作用，我们讨论控制它们的方法。我们的研究结果通过优化水合模式的结构，为将所需的传输特性设计到纳米离子器件中铺平了道路。