Superomniphobic Surfaces for Military Applications: Nano- and Micro- Fabrication Methods. Chapter 1: Lithographic Fabrication of Surfaces with Different Microgeometries and Investigation of Their Wetting Behaviour

摘要

Recent rapid improvements of micro/nanofabrication techniques have allowed us to prepare patterned surfaces with controlled topographic structures. In this report, three kinds of patterned surfaces, i.e., square, triangle and circle post array surfaces, have been prepared on silicon wafers. On such surfaces, for the same roughness or solid-liquid contact fraction value, different surface textures can exhibit completely different wetting behaviour. Effects of various microgeometrical parameters, such as length scale effect, edge/corner pinning effect, geometrical shape effect, direction-dependent effect, etc., on wetting have been investigated. For the patterned surfaces with fixed solid area fraction, a smaller microgeometrical length scale can induce a smaller advancing contact angle and a larger receding contact angle, when it is compared to a larger microgeometrical length scale. Competing factors such as solid area fraction and solid linear fraction are found to be responsible for such effect. Moreover, it is also revealed that there is a strong dependence of directions for surface wettability on the patterned surfaces. Different edge/corner pinning effects, including the pinning length and pinning point density, in various directions are suggested to be taken into consideration for affecting the surface wetting behaviour.