Adding roughness to hydrophilic surfaces is generally expected to enhance their wetting by water. Indeed, global free energy minimization predicts decreasing contact angles when roughness factor or surface energy increases. However, experimentally it is often found that water spreading on rough surfaces is impeded by pinning effects originating from local free energy minima; an effect, largely neglected in scientific literature. Here, we utilize Laplace pressure as a proxy for these local minima, and we map the transition to a superwetting state of hydrophilic nano-textured surfaces in terms of surface chemistry and texture geometry. We demonstrate the effect for polymer model surfaces templated from block-copolymer self-assembly comprising dense, nano-pillar arrays exhibiting strong pinning in their pristine state. By timed argon plasma exposure, we tune surface chemistry to map the transition into the superwetting state of low contact angle, which we show coincide with the surface supporting hemiwicking flow. For the near-ideal model surfaces, the transition to the superwetting state occurs below a critical material contact angle of ∼50°. We show that superwetting surfaces possess anti-fogging properties, and demonstrate long term stability of the superwetting effect by coating the nanotextured surfaces with ∼10 nm thin films of either tungsten or silica.

中文翻译：

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映射从嵌段共聚物自组装模板化的纳米纹理表面过渡到超湿状态†

通常期望增加亲水性表面的粗糙度以增强其被水润湿的能力。确实，当粗糙度系数或表面能增加时，总体自由能最小化预计接触角会减小。然而，从实验上经常发现，由于局部自由能极小值所引起的钉扎效应阻碍了水在粗糙表面上的扩散。一种在科学文献中基本上被忽略的效果。在这里，我们利用拉普拉斯压力代替这些局部极小值，并且根据表面化学性质和纹理几何形状，将过渡转变为亲水纳米纹理表面的超湿状态。我们展示了从嵌段共聚物自组装模板化的聚合物模型表面的效果，该嵌段共聚物自组装包括在原始状态下展现出强大钉扎作用的致密的纳米柱阵列。通过定时氩等离子体暴露，我们调整表面化学性质以映射到低接触角的超湿状态的过渡，这表明与支持半芯吸流动的表面相吻合。对于近乎理想的模型表面，在约50°的临界材料接触角以下会发生向超湿状态的过渡。我们表明，超湿表面具有防雾性能，并通过用〜10 nm的钨或二氧化硅薄膜覆盖纳米织构表面，证明了超湿效果的长期稳定性。