Courbin Laurent, Denieul Etienne, Dressaire Emilie, Roper Marcus, Ajdari Armand, Stone Howard A
School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Nat Mater. 2007 Sep;6(9):661-4. doi: 10.1038/nmat1978. Epub 2007 Aug 12.
Micropatterned surfaces have been studied extensively as model systems to understand influences of topographic or chemical heterogeneities on wetting phenomena. Such surfaces yield specific wetting or hydrodynamic effects, for example, ultrahydrophobic surfaces, 'fakir' droplets, tunable electrowetting, slip in the presence of surface heterogeneities and so on. In addition, chemical patterns allow control of the locus, size and shape of droplets by pinning the contact lines at predetermined locations. Applications include the design of 'self-cleaning' surfaces and hydrophilic spots to automate the deposition of probes on DNA chips. Here, we discuss wetting on topographically patterned but chemically homogeneous surfaces and demonstrate mechanisms of shape selection during imbibition of the texture. We obtain different deterministic final shapes of the spreading droplets, including octagons, squares, hexagons and circles. The shape selection depends on the topographic features and the liquid through its equilibrium contact angle. Considerations of the dynamics provide a 'shape' diagram that summarizes our observations and suggest rules for a designer's tool box.
微图案化表面作为模型系统已被广泛研究，用于理解地形或化学不均匀性对润湿现象的影响。这类表面会产生特定的润湿或流体动力学效应，例如超疏水表面、“苦行僧”液滴、可调电润湿、表面存在不均匀性时的滑移等等。此外，化学图案通过将接触线固定在预定位置，能够控制液滴的位置、大小和形状。应用包括“自清洁”表面和亲水点的设计，以实现DNA芯片上探针沉积的自动化。在此，我们讨论在地形图案化但化学均匀的表面上的润湿情况，并展示在纹理吸液过程中形状选择的机制。我们获得了不同的确定性最终形状的铺展液滴，包括八边形、正方形、六边形和圆形。形状选择取决于地形特征以及液体的平衡接触角。对动力学的考虑提供了一个“形状”图，总结了我们的观察结果，并为设计工具包提出了规则。
