Mechano-responsive and dynamic electro-wetting of replica-casted laser-induced periodic surface structures

目前的研究计划将材料合成方面（激光加工，复制铸造和表面功能化）与弹性体的机械响应润湿以及铁电聚合物的电，热和压电润湿相结合。我们的研究计划集中在柔性聚合物基材的动态润湿。为此，我们将在可拉伸聚合物表面实现特定的微纳米结构。润湿行为受表面功能化和各种外部触发因素的控制。这种微纳米结构是利用fs激光在金属基体上以所谓的激光诱导周期表面结构（LIPSS）的形式产生的。LIPSS模型随后在复制铸造过程中转移到柔性和可拉伸的聚合物样品中。在第一种方法中，亲水性和疏水性表面基团通过羟基化和选择性硅烷化的顺序过程耦合到结构表面。在与水接触时，制备的样品由于粗糙度引起的空气夹杂物而表现出超疏水行为。拉伸试样会降低接触角，因为粗糙度降低，亲水性官能团与水滴接触的数量增加。随着延伸时间的延长，由于极性基团比的增加，表面变得亲水。通过这种方式，聚合物的润湿性可以通过机械变形在大范围内可逆地调节。我们的第二种方法是基于极化铁电聚合物的电润湿。在这里，接触角可以通过水滴和衬底之间的外部电压来控制。根据所选聚合物的热或压电效应，可以通过温度或机械应力作为外部触发器来调节接触角。接触角的起点和最大工作范围由LIPSS模型确定，通过复制铸造过程将其转移到聚合物中。

The present research proposal combines material synthesis aspects (laser processing, replica casting, and surface functionalization) with the mechano-responsive wetting of elastomers and the electro-, pyro-, and piezo-wetting of ferroelectric polymers.Our research proposal focuses on the dynamic wetting of flexible polymer substrates. For this purpose we will realize specific micro- and nanostructures on the surface of stretchable polymers. The wetting behavior is controlled by surface functionalization and various external triggers. The micro- and nanostructures are produced on a metallic master substrate in the form of so-called laser-induced periodic surface structures (LIPSS) using an fs-laser. The LIPSS model is then transferred to flexible and stretchable polymer samples in a replica casting process.In a first approach, hydrophilic and hydrophobic surface groups are coupled to the structured surface by a sequential process of hydroxylation and selective silanization. In contact with water the prepared samples show superhydrophobic behaviour due to roughness induced air inclusions. Stretching the specimen reduces the contact angle as roughness is reduced and an increasing number of hydrophilic functional groups come into contact with the water drop. With prolonged elongation, the surface becomes hydrophilic due to the increasing specific amount of polar groups. In this way, the wettability of the polymer can be reversibly adjusted over a wide range by mechanical deformation.Our second approach is based on the electro-wetting of polarized ferroelectric polymers. Here the contact angle can be controlled by an external voltage between the water drop and the substrate. Based on the pyro or piezoelectric effect of the selected polymer, the contact angle can be adjusted by temperature or mechanical stress as an external trigger. The starting point of the contact angle and thus the maximum working range is determined by the LIPSS model, which is transferred to the polymer by the replica casting process.