For water droplets placed on a rough or structured surface, two distinct wetting states commonly observed are either the Wenzel state (droplets wet the surface without showing air pockets beneath the droplets) or the Cassie state (droplets reside on top of the structure with air pockets trapped beneath the droplets). Herein, we show molecular dynamics (MD) simulation evidence of a previously unreported wetting behavior, i.e., the rise of multiple Wenzel states on the structured surfaces whose flat-surface counterparts are superhydrophilic (i.e., complete wetting surfaces with the hallmark of zero contact angle for water droplets). Specifically, our MD simulations show that on the structured surfaces with topology of closed-loop nanowalls/nanochannels, the water droplet can exhibit multiple Wenzel wetting states with the apparent contact angles >0°. We name these distinct multiple Wenzel states as "topological wetting states" because their existence can be attributed to the topology of the closed-loop nanowalls/nanochannels. Regardless of the shape of the closed loops, such topological wetting states can always arise due to the topological invariant (i.e., all closed loops entail the same topological genus value). This unusual wetting behavior is contrary to the conventional view (and to the prediction of the Wenzel equation), namely, a rough hydrophilic surface should have stronger hydrophilicity than its flat-surface counterpart.

中文翻译：

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将超亲水表面变为弱亲水：拓扑润湿状态

对于放置在粗糙或结构化表面上的水滴，通常观察到的两种不同的润湿状态是 Wenzel 状态（水滴润湿表面而没有在水滴下方显示气泡）或 Cassie 状态（水滴位于具有气泡的结构顶部）被困在水滴之下）。在这里，我们展示了以前未报告的润湿行为的分子动力学 (MD) 模拟证据，即在结构化表面上出现多个 Wenzel 态，其平面对应物是超亲水的（即具有零接触角标志的完整润湿表面）为水滴）。具体而言，我们的 MD 模拟表明，在具有闭环纳米壁/纳米通道拓扑结构的结构化表面上，水滴可以表现出多种 Wenzel 润湿状态，并具有表观接触角 > 0°。我们将这些不同的多个 Wenzel 状态称为“拓扑润湿状态”，因为它们的存在可归因于闭环纳米壁/纳米通道的拓扑结构。不管闭环的形状如何，由于拓扑不变量（即，所有闭环都具有相同的拓扑属值），这种拓扑润湿状态总是会出现。这种不寻常的润湿行为与传统观点（以及 Wenzel 方程的预测）相反，即粗糙的亲水表面应该比其平坦表面具有更强的亲水性。由于拓扑不变量（即，所有闭环都具有相同的拓扑属值），这种拓扑润湿状态总是会出现。这种不寻常的润湿行为与传统观点（以及 Wenzel 方程的预测）相反，即粗糙的亲水表面应该比其平坦表面具有更强的亲水性。由于拓扑不变量（即，所有闭环都具有相同的拓扑属值），这种拓扑润湿状态总是会出现。这种不寻常的润湿行为与传统观点（以及 Wenzel 方程的预测）相反，即粗糙的亲水表面应该比其平坦表面具有更强的亲水性。