Focusing Effect for Sliding Drops Induced by Adaptive Surfaces

表面适应性已被提出是前进和后退接触角的速度依赖性的原因之一，即使在低滑动速度下。通过考虑干-湿和湿-干弛豫过程，我们提出了一个模型，该模型能够解释这些动态接触角（Langmuir 2018，34，11292）。我们的项目的目的是实验验证模型和探索，它是如何适用。在第一个资助期内，我们建立了一个倾斜的平面装置，用于测量高达1 m/s的水滴的前进和后退接触角与速度的关系。我们合成了一种无规聚（苯乙烯/丙烯酸）共聚物PS/AA，并证明了对于PS/AA膜上的水滴，推进接触角-速度-曲线确实可以与模型拟合。拟合揭示了聚合物在表面处的弛豫时间< 2 ms。然而，我们仍然缺少对干-湿弛豫时间的独立测量，这是模型完全验证所必需的。第二个资助期的目的是研究聚合物表面，在那里我们可以独立地测量干-湿和湿-干转变的弛豫时间。然后，记录的前进接触角与速度的依赖关系可以独立地使用我们的模型进行验证。因此，我们计划合成三种类型的聚合物刷：（1）PS和聚（2-乙烯基吡啶）（PVP）二元刷膜，（2）pH响应性聚（N，N-二甲基氨基乙基甲基丙烯酸酯）（PDMAEMA）刷和（3）不同的嵌段共聚物层。对于在自适应表面上滑动的一系列液滴，我们预测了聚焦效应。它是由第一滴沿表面沿着滑动引起的部分适应引起的。这一液滴留下了一条表面能增加的通道，我们预计随后的液滴将沿着同一通道滑动。我们的目标是验证这一假设。

Surface adaptation has been put forward to be one cause for the velocity dependence of advancing and receding contact angles, even at low slide velocity. By considering a dry-to-wet and a wet-to-dry relaxation process, we had proposed a model, which is able to explain these dynamic contact angles (Langmuir 2018, 34, 11292). The aim of our project is to experimentally verify the model and explore, how applicable it is. In the first funding period, we built an inclined plane setup to measure advancing and receding contact angles versus velocity for water drops up to 1 m/s. We synthesized a random poly(styrene/acrylic acid) copolymer PS/AA and demonstrated that for water drops on PS/AA films, advancing-contact-angle-versus-velocity-curves can indeed be fitted with the model. The fit revealed relaxation times < 2 ms of the polymer at the surface. However, we are still missing independent measurements of the dry-to-wet relaxation times, which would be required for full validation of the model. The aim for the second funding period is to investigate polymer surfaces, where we can independently measure the relaxation time of the dry-to-wet and the wet-to-dry transitions. Then, recorded advancing-contact-angle-versus-velocity-dependencies can be validated independently using our model. Therefore, we plan to synthesize three types of polymer brushes: (1) PS and poly(2-vinylpyridine) (PVP) binary brush films, (2) pH-responsive poly(N,N-dimethyl aminoethyl meth¬acrylate) (PDMAEMA) brushes and (3) different block copolymer layers. For series of drops sliding on an adaptive surface we predicted a focusing effect. It is induced by partial adaptation caused by the first drop sliding along the surface. This drop leaves behind a lane of increased surface energy and we expect that subsequent drops will then slide along the same lane. Our aim is to verify this hypothesis.