Dynamic Wetting of Adaptive and Responsive Polyelectrolyte Substrates: A multiscale approach

在细胞或蛋白质等与生物相关的系统的粘附性的背景下，通过水溶液润湿聚合物基质是特别重要的，但对于润湿的技术控制也是特别感兴趣的。含有电荷或极性基团的聚合物基质在水中有很强的膨胀倾向。因此，影响润湿性能的不仅有基材的弹性，还包括基材的适应性。本项目的总体目标是了解聚电解质基质的适应性/响应性与其动态润湿性能之间的关系。在本项目中，适应是指由于(部分)吸收水或含水盐溶液的润湿液体而引起的聚电解质基材的膨胀。一类被研究的自适应衬底对温度具有响应性，这提出了一个问题：温度的变化如何影响润湿特性。在这种情况下，该项目旨在更好地理解纳米/介观长度尺度(10 nm-1m)横向和垂直于三相接触线(TPCL)表面的润湿现象。因此，将使用原子力显微镜技术。为了与宏观长度尺度上的润湿现象相联系，还将进行典型的静态和动态润湿实验(即固定滴落、倾斜平板上的滴落、前进和后退接触角测量)。表面效应，如表面弹性、表面电荷和界面分子重排，被认为是纳米/介观尺度上影响宏观润湿现象的滞后效应。在纳米尺度上可能发生三种类型的表面变形，并可能对TPCL的整体轮廓做出贡献：1)液滴前方由分离压力控制的前驱薄膜，2)由于液体从液滴向衬底表面横向(和垂直)输送到衬底中而形成的膨胀衬底边缘，以及3)由于表面应力的垂直分量而诱导的润湿脊。该项目旨在解开不同表面对润湿现象的影响。两者都可以被认为是凝胶。这两种类型的衬底在它们的优势方面是互补的，并允许控制表面电荷(符号、密度)、可实现的厚度范围、机械和流变性、亲水性/亲水性平衡以及它们对温度的响应。计划在SPP内与实验学家和理论家合作，以便更深入地了解不同长度尺度上的湿润现象之间的联系。

Wetting of polymer substrates by aqueous solutions is of specific interest in the context of the adhesion of biologically relevant systems like cells or proteins, but also for the technical control of wetting. Polymer substrates which contain charges or polar groups have a strong tendency to swell in water. Therefore, not only elastic but also adaptive properties of the substrate affect the wetting properties. The global aim of the present project is the understanding of the relation between the adaptation/response of polyelectrolyte substrates and their dynamic wetting properties. In the present project adaptation refers to swelling of the polyelectrolyte substrate caused by the (partial) uptake of the wetting liquid which is water or an aqueous salt solution. One class of studied adaptive substrate is responsive to temperature, which raises the question how a change in temperature affects wetting properties.In this context the project aims to contribute to a better understanding of wetting phenomena on nanoscopic/mesoscopic length scale (10 nm - 1 m) lateral and vertical to the surface close to the three-phase contact line (TPCL). Therefore, AFM techniques will be used. To make a link to wetting phenomena on a macroscopic length scale, typical static and dynamic wetting experiments (i.e. sessile drop, drop on a tilted plate, advancing and receding contact angle measurements) will be also carried out. Surface effects like surface elasticity, surface charge and interfacial molecular rearrangement are assumed to govern hysteresis effects on a nano/mesoscale which affects macroscopic wetting phenomena. Three types of surface deformation might occur on the nanoscale and might contribute to the overall profile of the TPCL: 1) A precursor film in front of the droplet, which is dominated by the disjoining pressure, 2) a rim of swollen substrate which is due to transport of liquid from the droplet into the substrate lateral (and vertical) to the substrate surface and 3) a wetting ridge induced by vertical components of the surface stress.The project aims to disentangle the different surface effects on wetting phenomena.As polyelectrolyte substrates polyelectrolyte multilayers (PEMs) and layers/multilayers of adsorbed PNIAPM microgel are used. Both can be considered as gels. Both types of substrates are complementary with respect to their advantages and allows control of surface charge (sign, density), range of achievable thickness, mechanical and rheological properties, hydrophilic/hydrophilic balance and their response to temperature. Cooperations are planned within the SPP with experimentalists and theoreticians in order to get deeper insight into the link between wetting phenomena on different length scales.