An Investigation of How Hydrophobicity, Water, and Surface Topography Influence Macroscopic Particle Accumulation on Surfaces : A Case Study of Grass Accumulation on Robotic Lawn Mower

Abstract: This master's thesis project investigates the impact of hydrophobicity and topology on dry and wet macroscopic particle accumulation on surfaces. The report begins by outlining the challenges associated with this phenomenon and the existing theories and methods used to study it, including adhesion, surface engineering, the Lotus effect, and humidity. The method chapter presents the case study of grass accumulation for robotic lawn mowing application and describes experiments conducted to simulate the accumulation of grass during robotic lawn mowing. These experiments explore two different phenomena: the accumulation of grass that is already stuck to a surface and the process by which grass initially sticks to a surface. Experiments have been done to change the hydrophobicity level of certain specimens and investigate how hydrophobicity and humidity affect the stickiness of grass when already accumulated on a surface. In addition, experiments are conducted by throwing grass towards surfaces with different hydrophobicity and topology to determine the influence of these variables on accumulation. Finally, a physical field test is conducted. The findings indicate that hydrophobicity up to 108,2° water contact angle has a low impact on both static and dynamic grass accumulation. Increased hydrophobicity does not tend to decrease grass accumulation, even showing increased accumulation in some experiments. Humidity and the wetness of the grass are more important factors. Experiments have shown that a textured surface can decrease the accumulation, showing significant results in a controlled environment. However, these results did not transfer over in a significant way to a real robotic lawn mowing situation.