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，允许人们通过电位来控制电解液的润湿能量。因此，可以调节液滴形状和表面上的液体扩散动力学，然而，通过纳米孔内液体半月面的电势依赖曲率，也可以控制对多孔表面的渗吸。此外，纳米孔受限液体的巨大拉普拉斯压力和流固界面应力会引起多孔固体的显著变形，从而导致液体毛细作用和固体弹性的电润湿耦合，即电可切换弹性毛细作用。到目前为止，这些现象(液滴形状动力学、吸胀和变形行为)之间的复杂相互作用几乎没有人研究过。在这里，我们建议从实验上探索电解液在单晶硅表面上的润湿动力学，以及固体在固-液界面张力的电势控制下的弹性变形。应研究在纳米孔表面使用介质氧化层的直接润湿和电润湿。通过随时间变化的液滴形状分析、光流干涉仪、膨胀仪和同步辐射原位X射线衍射仪，在改变表面平均孔径和孔隙率的情况下，考察了前驱膜的存在、液滴的扩散和渗吸动力学以及微观(原子硅晶格)和宏观(衬底)尺度上的变形。这些实验应与本优先计划中的项目密切合作进行分析，重点放在计算模型和液体在平面和多孔表面上的扩散、渗吸和弹性毛细的介观唯象理论上。该项目的首要目标是对纳米孔表面的电可切换静态和动态润湿有一个基本的、可预测的了解。

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.