Microstructure and wettability character of nepenthes' pitcher surfaces

Nepenthes' pitchers are marvelous leaves working as insect traps which is mainly caused by the inner surfaces. While the wettability of the inner pitcher surface is still a lack of in-depth research. Through various measuremtns of the contact angle of Nepenths' pitcher surfaces, it was found that the slippery zone is hydrophobic with the maximum contact angle (150 ± 2)° and the digestive zone is hydrophilic with the minimum contact angle (16 ± 2)°, and there exists an obvious wettability dividing line between slippery zone and digestive zone. Micro-and nanoscale hierarchical structures are present on the slippery zone, while a microscale hierarchical structure is present on the digestive zone. The effect of the material composition and microstructure of the inner surfaces on wettability were analysed through chemical treatment and bio-replication. The results show that hydrophobic of the slippery zone is mainly caused by the wax on pitcher surface and hydrophilic of the digestive zone may be caused by some kinds of hydrophilic materials. The large span of wettability between slippery zone and digestive zone is depend on both its chemical composition and its surface morphology. This research may provide a reference for the design of slippery surfaces.