Substrate and Drop Dynamics During Impact and Coalescence on Soft Adaptive Surfaces

水滴撞击柔软材料在日常生活中经常遇到，例如，淋浴时水滴落在皮肤上，水滴撞击在新油漆或植物叶子上，或者只是水滴撞击在先前潮湿的表面上。这样的系统通常由（薄的）软的和自适应的表面层在坚硬的基材上组成。软层无论有多薄，都能在微观和宏观尺度上改变接触线的行为，尤其是液滴的行为。与此相反，迄今为止的研究主要集中在硬表面、液池和混相液表面层（通常是非微观深度）。粘弹性基底上液滴静态形状的耦合问题已经被广泛地建模，并且相对缓慢的接触线运动过程已经得到了解决。最近的研究主要集中在研究软基材与快速移动的接触线之间的相互作用，例如在跌落冲击过程中遇到的接触线。然而，在这些研究中，虽然基材的动力学是所有宏观接触线和液滴行为变化的实际原因，但基材的实际动力学并没有被记录和分析——在快速过程中测量薄表面层的微观变形需要大量的实验努力和复杂的新技术。我的项目涉及两个典型的过程，水滴对柔软柔性层的影响和有限深度的流体层上的水滴聚结。所述底物可由粘性或粘弹性液体或粘弹性凝胶组成。标准侧视和顶/底视高速成像将与许多非标准高速底视技术相结合，提供对基板变形、应变或表面与液体接触形成过程的访问，以及可能夹带的微观气体层。我的设置和专业知识将通过合作提供给SPP-2171的其他参与小组，目前计划用于几种自适应基板。我将与理论家合作，对我的实验进行分析和数值模拟。

Droplets impacting on soft materials are frequently encountered ineveryday life, e.g. water drops on skin during showering, dropsimpacting on fresh paint or on plant leaves, or simply drops impacting onto a previously wetted surface. Such systems often consist of a (thin) soft and adaptive surface layer on a stiff substrate. The soft layer, however thin, can crucially alter the behavior of contact lines, and particularly of droplets, on microscopic and macroscopic scales. Contrasting to this, research so farmainly focused on hard surfaces, liquid pools and miscible liquid surface layers (of usually non-microscopic depth). The coupled problem of static shapes of a droplet on visco-elastic substrates has been modeled extensively, and comparatively slow processes of contact line motion have been addressed. Recent research develops more towards studies of the interaction ofsoft substrates with rapidly moving contact lines, as e.g. encountered during drop impact. However, in those studies, the dynamics of the substrate, while it is the actual reason for all changes of the macroscopic contact line and droplet behavior, the actual substrate dynamics is not recorded and not analyzed – measuring the microscopic deformations of thin surface layers during rapid processes requires substantial experimental effort and sophisticated, new techniques. My project deals with two exemplary processes, drop impact on soft flexible layers and drop coalescence on fluid layers of limited depth. The substrates may consist of viscous, or viscoelastic liquids, or of viscoelastic gels. Standard side and top / bottom view high-speed imaging will be combined with a number of non-standard high-speed bottom view techniques,providing access to the substrate's deformations, strains or contact formation processes of the surface with the liquid, as well as possibly entrained microscopic gas layers. My setup and expertise will beavailable to the other participating groups of SPP-2171 throughcollaboration, currently planned for several adaptive substrates. I willcollaborate with theoreticians on analytical and numerical modeling ofmy experiments.