Gao Yurui, Zhu Chongqin, Zuhlke Craig, Alexander Dennis, Francisco Joseph S, Zeng Xiao Cheng
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States.
Department of Earth and Environmental Science, and Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
J Am Chem Soc. 2020 Oct 28;142(43):18491-18502. doi: 10.1021/jacs.0c07224. Epub 2020 Oct 15.
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.
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文策尔状态（水滴润湿表面，水滴下方没有气穴）或卡西状态（水滴位于结构顶部，水滴下方困住气穴）。在此，我们展示了一种先前未报道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种文策尔状态，其对应的平面表面是超亲水的（即完全润湿表面，水滴的接触角为零）。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，水滴可以呈现出表观接触角大于0°的多种文策尔润湿状态。我们将这些不同的多种文策尔状态命名为“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。无论闭环的形状如何，由于拓扑不变性（即所有闭环都具有相同的拓扑亏格值），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（以及文策尔方程的预测）相反，即粗糙的亲水表面应该比其对应的平面表面具有更强的亲水性。
