Microscopic Mechanisms and Surface Adaptation Effects in Slide-Electrification

滑动电气化描述了在移动的液滴和疏水表面之间的自发电荷分离。根据衬底材料和液体的不同，液滴会积累正电荷或负电荷，而衬底则相反。在这里，水滴电荷会受到表面与水滴的接触时间以及后续水滴之间的时间的影响。因此，描述电荷产生的模型包括一个表面适应术语，非常类似于湿润适应现象。滑块通电的微观起源和表面适应效应尚不清楚。该机制在现象学上得到了合理化，假设在后退接触线上电荷钉住。在这里，电子转移、离子的吸附/解吸或双电层的不完全重组都可能导致观察到的效应。因此，我们项目的第一个目标是对幻灯片通电的分子理解。我们将结合实验和计算机模拟，系统地改变固液界面，通过改变涉及的三个组成部分：1)底物，2)疏水层，3)和液体（液体类型，盐浓度，pH值）。对于衬底而言，介电常数和表面化学性质是导致滑动起电的重要因素。为了研究离子和电子电荷转移对玻片电气化过程的贡献，我们还将包括具有定义的电子导电性的碳基模型表面。为了控制接枝密度和电荷在表面的扩散，我们将改变疏水层的分子量和表面粗糙度。此外，我们将改变表面化学，例如氢氧化物和胺功能化表面。为了研究润湿适应和电荷适应之间的相互作用，我们将与该SPP中的其他小组合作研究自适应聚合物和聚电解质表面。因此，我们希望阐明在三相接触线上形成的电压和表面适应背后的机制。滑动电气化的应用是发电，是一种潜在的可再生能源。目前，从液滴动能到电能的能量转换效率非常低：远低于0.1%。因此，该项目的第二个目标是了解滑梯电气化效率的基本限制。我们希望确定基材-表面层-液体组合，以提高转换效率。这将通过计算预先筛选表面组合来实现，目标是最大化表面电压和滴电荷。然后将对表现最佳的组合进行实验表征。

Slide electrification describes a spontaneous charge separation between a moving liquid droplet and a hydrophobic surface. Depending on substrate material and liquid, the drop accumulates either positive or negative charge with the substrate charging oppositely. Here, the drop charge can be influenced by the contact time between surface and water drop and the time between subsequent drops. Models, that describe the charge generation, therefore include a surface adaptation term, very much akin to wetting adaptation phenomena. The microscopic origin of slide electrification and the surface adaptation effects is still unclear. The mechanism has been rationalized phenomenologically, assuming charge pinning at the receding contact line. Here, electron transfer, adsorption/desorption of ions, or an incomplete reorganization of the electric double layer could all lead to the observed effects. Thus, the first goal of our project is a molecular understanding of slide electrification. We will combine experiments with computer simulations and systematically change the solid-liquid interface by varying the three components that are involved: 1) the substrate, 2) the hydrophobic layer 3) and the liquid (type of liquid, salt concentration, pH). For the substrate, the dielectric permittivity and surface chemistry are the important factors contributing to slide electrification. To investigate the contribution of ionic and electronic charge transfer to the slide electrification process, we will also include carbon-based model surfaces with defined electronic conductivity. To control the grafting density and the charge diffusion at the surface, we will change the molecular weight of the hydrophobic layer and the surface roughness. In addition, we will vary the surface chemistry, e.g. with hydroxide and amine functionalized surfaces. To study the interplay between wetting adaptation and charge adaptation, we will study adaptive polymeric and polyelectrolyte surfaces in cooperation with other groups within this SPP. Thus, we want to clarify the mechanisms behind the voltage that forms at the three-phase contact line and the surface adaptation. The application of slide electrification is electricity generation, a potential source of renewable energy. Currently, the efficiency of energy conversion from kinetic droplet energy to electric power is very low: much less than 0,1 %. Therefore, the second goal of the project is to understand the fundamental limits of the slide electrification efficiency. We want to identify substrate – surface layer – liquid combinations that yield improved conversion efficiencies. This will be achieved by computational pre-screening of surface combinations, aiming at those that maximize the surface voltage and the drop charge. The top performing combinations will be then characterized experimentally.