Dynamic Electrowetting at Nanoporous Surfaces: Switchable Spreading, Imbibition, and Elastocapillarity

导电衬底，如纳米多孔金属和半导体的表面，允许人们通过电势来控制电解质的润湿能。因此，有可能调整液滴形状和液体在表面上的扩散动力学，然而，通过纳米孔内液体半月板的电位依赖曲率，多孔表面的吸吮受到外部控制。此外，巨大的拉普拉斯压力和流固界面应力（典型的纳米孔限制液体）会引起多孔固体的明显变形，从而导致液体毛细与固体弹性的电位依赖耦合的电润湿，即电可切换的弹性毛细。这些现象（液滴形状动力学、吸胀和变形行为）之间复杂的相互作用迄今为止几乎没有被探索过。在这里，我们提出通过实验来探索水电解质在由平行排列的管状纳米孔穿过的定制单晶硅表面上的润湿动力学，以及在固液界面张力的电势控制下固体的密切相关的弹性变形。应研究在纳米孔表面使用介电氧化物层的直接润湿和电润湿。前驱体膜的存在、液滴的扩散和吸胀动力学以及微观（原子硅晶格）和宏观（衬底）尺度上的变形将通过随时间变化的液滴形状分析、光流体干涉测量、膨胀测量和基于同步加速器的原位x射线衍射来研究。实验应与本优先项目密切合作进行分析，重点研究平面和多孔表面液体扩散、吸胀和弹性毛细管的计算模型和介观现象学理论。该项目的总体目标是对纳米多孔表面上可电切换的静态和动态润湿现象有一个基本的、预测性的理解。

Electrically conductive substrates, such as surfaces of nanoporous metals and semiconductors allow one to control the wetting energies of electrolytes by electrical potentials. Thereby, it is possible to tune droplet shape and liquid spreading dynamics at surfaces, however also the imbibition into the porous surface is under external control via electrical potential-dependent curvatures of the liquid menisci within the nanopores. Moreover, the enormous Laplace pressures and fluid-solid interfacial stresses, typical of nanopore-confined liquids, induce noticeable deformations of the porous solids, and thus result in the case of electrowetting in a potential-dependent coupling of liquid capillarity with solid elasticity, i.e. electrically switchable elastocapillarity. The complex interplay of these phenomenologies (droplet shape dynamics, imbibition and deformation behaviour) have been barely explored to date. Here, it is proposed to explore experimentally the wetting dynamics of aqueous electrolytes at tailored, single-crystalline silicon surfaces traversed by a parallel array of tubular nanopores along with the intimately related elastic deformation of the solids under electrical potential control of the solid-liquid interfacial tension. Both direct and electrowetting with dielectric oxide layers at the nanopore surfaces shall be studied. The existence of precursor films, droplet spreading and imbibition dynamics as well as the deformation on the microscopic (atomic silicon lattice) and macroscopic (substrate) scale will be scrutinized by time-dependent droplet shape analysis, opto-fluidic interferometry, dilatometry and synchrotron-based in-situ x-ray diffraction under variation of the mean pore diameter and porosity of the surface. The experiments shall be analysed in close cooperation with projects in this priority program focusing on computational modelling and mesoscopic phenomenological theories for liquid spreading, imbibition and elastocapillarity at planar and porous surfaces. The overarching objective of this project is a fundamental, predictive understanding of electrically switchable static and dynamic wetting at nanoporous surfaces.