Improved condensation on hierachically structured surfaces

微结构表面上可控的液滴凝结增强了传热。为了实现这一目标，我们将结合具有极低接触角滞后的条状表面结构和一组用于单个液滴形成的集成微结构隔室。当冷凝过程中液滴尺寸超过阈值时，后者通过条形线清除。通过在带线之外的冷凝室的集成，防止了连续流体膜的产生。隔间的几何形状和尺寸需要优化，以产生小液滴，以改善传热。液滴的大小和速度将由在空气中稍微降低温度的光学成像装置来确定。利用相同的设置来评估冷凝过程中由于液滴直径超过给定表面结构的阈值而在条形线上上升的液滴的脱湿过程。在传热过程的理论建模过程中，这些液滴种群数据对于确定给定装置的热通量是必要的。液滴传输的动力学可能是由已经运动的液滴与仍保留在结构上的液滴的结合所支持的，从而导致沿带状的横扫效应。这些热交换板的整体效率将通过在实际工业条件下操作的第二个实验装置进行研究。所有的研究都将首先使用硅作为基础材料，因为微结构工艺已经在TUK的洁净室设施中可用。由于其工业相关性，优化的表面结构将以共同的作用转移到高温聚合物的表面。为此，制备了负表面结构的硅母片，并用于将所需的结构压印到聚合物表面。这些工艺需要根据所涉及表面的化学性质进行优化，以通过压印转移纳米结构，并促进主聚合物和底层聚合物的分离。最后一个项目部分致力于研究层次表面结构是否通过与超疏水和-或超亲水纳米结构结合来提高换热板的效率。用于生成所需纳米结构的技术需要适用于所使用的材料，其范围可以从黑硅的等离子体刻蚀直接激光写入聚合物纳米结构到等离子体刻蚀期间使用自旋涂层纳米材料作为硬掩膜的聚合物干刻蚀。总的来说，新开发的混合结构在其他技术应用中具有广泛的潜力，这些技术应用需要非润湿性（从管道-面霜，番茄酱等流出）。

Controlled generation of droplet condensation on microstructured surfaces enhances heat transfer. To achieve this we will combine strip-like surface structures with exceedingly low contact angle hysteresis with a set of integrated microstructured compartments exploited for individual droplet formation. The latter are cleared via the strip lines when the droplet dimension during the condensation process exceeds a threshold value. Through the integration of the condensation compartments besides the strip lines the generation of a continuous fluid film is prevented.The geometry and dimensions of the compartments need to be optimized to generate small droplets to improve heat transfer. The droplet size and velocity will be determined by an optical imaging set-up operated at slightly reduced temperatures in air. The same set-up is exploited to evaluate the dewetting process of droplets that are lifted up on the strip lines during condensation because their diameter exceeds the threshold value of the given surface structure. These droplet population data are necessary during the theoretical modelling of the heat transfer process to determine the thermal throughput of the given set-up. The dynamics of droplet transport is presumably supported by coalescence of already moving droplets with those still retained on the structure, leading to a sweeping effect along the strips. The overall efficiency of these heat exchange plates will be investigated with a second experimental set-up that is operated under real i.e. industrial conditions.All investigations will be first started using silicon as base material because the microstructuring processes are already available at the clean room facility of TUK. The optimized surface structures will then be transferred in a common action onto the surface of high-temperature polymers due to their industrial relevance. For this purpose, silicon masters of the negative surface structures are prepared and used to emboss the desired structure into the polymer surface. These processes need to be optimized with respect to the chemical nature of the involved surfaces to transfer nanostructures by embossing and facilitate the separation of the master and underlying polymer.The last project part is devoted to the question whether hierarchical surface structures improve the efficiency of the heat exchange plate by combining them with superhydrophobic and - or superhydrophilic nanostructures. The techniques used to generate the desired nanostructures need to be adopted to the material in use and may range from plasma etching of black silicon over direct laser writing of polymeric nanostructures to dry etching of the polymer using spincoated nanoscopic materials as a hard mask during plasma etching. Overall, the newly developed hybrid structures have a wide potential in other technical applications were non-wetting is desired (efflux from tubes - creams, ketchup, etc.).