Hierarchical Structured Superhydrophobic Surfaces on Graphite Composites

A scalable thermal imprinting method and subsequent hierarchical structuring with metal oxide nanostructures forms superhydrophilic or superhydrophobic surfaces on graphite composites. Anisotropically etched silicon wafers serve as basis to create various microstructures by a thermal imprinting on thermally conductive polymer graphite composites. Even after 32 times of embossing, the mold can be reused and restored by pyrolysis, ensuring its longevity and costeffective process. Nanostructuring caused by sputtered aluminum or electron beam evaporated copper on the embossed microstructures and further oxidized with a simple hot water treatment offers a wide range of different hierarchical structures. The combination of microstructures and nanostructures with a low surface energy coating of stearic or lauric acid results in a superhydrophobic surface, which is completely water-repellent with a contact angle greater than 160° and low contact angle hysteresis lower than 5°. This work provides a deeper understanding of the effects of the interaction of aluminum and copper metal oxide nanostructures and thermally imprinted microstructures on surface of graphite compounds. It has been demonstrated that superhydrophobic surfaces can be created with both fatty acids. Lauric acid is easier to use due to its simple handling and reaches a maximum contact angle after 30 min of exposure time with copper oxide nanostructures of over 170°.