Dynamic wetting phenomena and contact angle hysteresis of drops on polymer brushes and gels

沉积在聚合物刷子或凝胶上的液滴被润湿的隆起包围。原因是所涉及的界面力的垂直分量将刷子/凝胶向上拉起。凸脊的形状和高度对液滴在表面上运动的接触角和摩擦力有很大影响。我们的目标是了解动态接触角、移动液滴引起的脊线重组以及由此产生的粘性耗散机制。为了获得与这些动态润湿现象有关的详细物理信息，我们打算将激光扫描共聚焦显微镜和粗粒度分子动力学模拟结合起来。我们打算将重点放在以下模型体系上：(I)聚合物凝胶。在这里，我们将研究硅油渗透的PDMS凝胶。将使用水凝胶进行比较。我们计划改变凝胶的厚度和交联度，渗透液体的粘度和液滴在表面上的运动速度。(Ii)PDMS刷子带有和不带有浸没的游离聚合物链。初步的实验研究表明，电刷中自由链的存在对沉积液滴的动态特性有显著影响，特别是对接触角滞后的影响。根据电刷的类型和自由链的数量，接触角有很大的不同。这为通过简单的物理机制控制聚合物刷子表面的润湿性能开辟了新的途径。

Droplets deposited on polymer brushes or gels are surrounded by a wetting ridge. The reason is that the vertical component of the involved interfacial forces pulls the brush/gel up. The shape and height of the ridge greatly influence the contact angles and friction of drops moving on the surface. We aim to understand the dynamic contact angles, the reorganization of the ridge caused by the moving drops and the resulting mechanisms of viscous dissipation. To gain detailed information on the physics involved in these dynamic wetting phenomena, we intend to combine laser scanning confocal microscopy and coarse grained molecular dynamic simulations. We intend to focus on the following model systems: (i) Polymer gels. Here we will study PDMS gels infiltrated by silicone oil. Hydrogels will be used for comparison. We plan to vary the thickness and the crosslinking density of the gel, the viscosity of the infiltrated liquid and the velocity of the drop moving on the surfaces. (ii) PDMS brushes with and without immersed free polymer chains. Preliminary experimental studies have shown that the presence of free chains in the brush has a significant impact on the dynamic properties of deposited droplets, and, in particular, on the contact angle hysteresis. Depending on the type of brush and amount of free chains the contact angle varies greatly. This opens new avenues for controlling the wetting properties of polymer brush surfaces by simple physical mechanisms.