Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.
ACS Appl Mater Interfaces. 2012 Jan;4(1):123-30. doi: 10.1021/am201104q. Epub 2011 Dec 27.
In order to study the influence of surface chemistry on the wetting of structured surfaces, microstructures consisting of grooves or squares were produced via hot embossing of poly(ethylene-alt-tetrafluoroethylene) ETFE substrates. The structured substrates were modified with polymer brushes, thereby changing their surface functionality and wettability. Water droplets were most strongly pinned to the structure when the surface was moderately hydrophilic, as in the case of poly(4-vinylpyridine) (P4VP) or poly(vinyl(N-methyl-2-pyridone) (PVMP) brush-modified substrates. As a result, the droplet shape was determined by the features of the microstructure. The water contact angles (CA) were considerably higher than on flat surfaces and differed, in the most extreme case, by 37° when measured on grooved substrates, parallel and perpendicular to the grooves. On hydrophobic substrates (pristine ETFE), the same effects were observed but were much less pronounced. On very hydrophilic sampes (those modified with poly(N-methyl-vinylpyridinium) (QP4VP)), the microstructure had no influence on the drop shape. These findings are explained by significant differences in apparent and real contact angles at the relatively smooth edges of the embossed structures. Finally, the highly anisotropic grooved microstructure was combined with a gradient in polymer brush composition and wettability. In the case of a parallel alignment of the gradient direction to the grooves, the directed spreading of water droplets could be observed.
为了研究表面化学对结构化表面润湿性的影响，通过热压印聚（乙烯-共-四氟乙烯）（ETFE）基底来制备由沟槽或正方形组成的微结构。通过聚合物刷对结构化基底进行改性，从而改变其表面功能和润湿性。当表面具有适度亲水性时，例如在聚（4-乙烯基吡啶）（P4VP）或聚（N-甲基-2-吡啶酮）（PVMP）刷改性基底的情况下，水滴被最强地固定在结构上。因此，液滴形状由微结构的特征决定。水接触角（CA）远高于平面基底，在测量沟槽基底时，平行和垂直于沟槽的情况相差 37°，在极端情况下相差 37°。在疏水性基底（原始 ETFE）上，观察到相同的效果，但不那么明显。在非常亲水的样品（用聚（N-甲基-乙烯基吡啶鎓）（QP4VP）改性的样品）上，微结构对液滴形状没有影响。这些发现可以通过压印结构相对光滑边缘的表观和真实接触角的显著差异来解释。最后，高度各向异性的沟槽微结构与聚合物刷组成和润湿性的梯度相结合。在梯度方向与沟槽平行对齐的情况下，可以观察到水滴的定向扩展。
