Functional Surfaces with Liquid Diode Characteristics

What if, the mantle of a pill investigated the contents of the stomach or the intestine to find pathogens? Vaccines were given painlessly though the skin using a plaster? What if, a diaper conducted urine against gravity away from the babys bum and was bio-degradable? What if, the skin of robots absorbed liquid from the surroundings and processed it? Thats all still up in the air. However, guiding liquids in a defined way plays a significant role in several fields of engineering. Currently, water and other liquids are conducted to heated components for cooling and oils lubricate bearings to reduce friction. The project targets more efficient, low-cost, high-performance liquid management on surfaces and uses peculiar polymers to open up new fields of application. Nature serves as source of inspiration since animals developed strategies to guide liquids in a specific direction. Most interesting, certain lizards, bugs and fleas, use a passive transport mechanism, i.e. no energy is consumed. For this purpose, they employ microchannels that change their cross-sections periodically, whereby this variation is different in the forward and backward direction. Remarkably, the liquid flows in a preferential direction even against gravity. In analogy to electronics, the term liquid diodes is used for devices which transport liquid directionally. The question arises as to whether this functional principle is applicable to flexible, stretchable or even bio-degradable and edible surfaces. If the answer is yes, then there is a need to investigate how the properties of the materials will influence liquid transport, e.g., whether it will continue to flow in only one direction, if the device is bent or stretched. In doing so, robust halting mechanisms in the backward direction are crucial. Despites it is particularly interesting, if liquids can flow directionally in capillaries devoid of a floor and a ceiling. This would increase the contact area with the surroundings and such chemical and physical exchange. In addition, natural role models can trigger liquid transport by muscle movement. Accordingly, control mechanisms will be integrated: Chemicals, tensile forces or electrical voltage will trigger directional flow. In answering the above research questions, a model-based approach is used to tailor the capillary channel dimensions to specific liquid-material-combinations. Demonstrators will serve as proof of concepts; they will be fabricated by state-of-the-art technologies such as 3D printing and laser-ablation as well as by established ones such as casting. Structure quality will be surveyed by microscopic methods, e.g. by optical coherence tomography. For characterization, a custom-tailored algorithm will calculate wetted area, distance travelled, asymmetry of wetting and its contours relative to time from videos. The influences of bending, stretching, gravity, electrical voltage and chemical composition on these parameters will be studied.