Fabrication Of Superhydrophobic Surfaces With Multi-scale Structure And Their Wettability Under Condensation

Superhydrophobic surfaces have drawn attention of scientists fromvarious fields due to their excellent properties, such as self-cleaning,anti-corrosion, drag-reduction, and so on. Many effects have beendevoted to the study of fabrication and properties of superhydrophobicsurfaces. However, only a few studies reported whether superhydrophobicsurface can retain superhydrophobicity under any condition. Lately, somescientists found that superhydrophobic surfaces may losesuperhydrophobicity under condensation. The lost of superhydrophobicitymeans other fine properties of superhydrophobic surface will lose as well.Thus, we explored the relationship between the multi-scale structure andthe wettability of superhydrophobic surfaces under condensation, and tryto discover the rule. The main contents are as follows:(1) Two type of LDPE coatings were obtained by a simple and novelapproach, the surface structure of which were different. One of them issuperhydrophobic LDPE coating with high sliding angle and the other issuperhydrophobic LDPE coating with low sliding angle. Then thewettability test of these two type superhydrophobic LDPE coating andsmooth LDPE coating were performed under condensation. The resultsshow that the water repellency of the superhydrophobic LDPE coatingwith low sliding angle is much better than the superhydrophobic LDPEcoating with high sliding angle, while the water repellency of thesuperhydrophobic LDPE coating with high sliding angle is only a littlebetter than the smooth LDPE coating. The result also indicates that thechange of hierarchical structure on superhydrophobic surface willinfluence the surface wettability under condensation.(2) We chose five kinds of superhydrophobic surfaces with differentsurface structure in nature, namely lotus leaf, bamboo leaf, China rose,taro leaf and setcreasea purpurea leaf, and observed the wettability changeand the condensation behavior of these hydrophobic surfaces undercondensation, and we found that only the setcreasea purpurea leaf surfacecan keep hydrophobic property under condensation.(3) To further understand how the micro structure affect the wettability change of superhydrophobic surfaces under condensation, wecopied the hierarchical structure of lotus leaf, bamboo leaf, China rose,taro leaf and setcreasea purpurea leaf onto paraffin surface by templatemethod, and then studied the wettability change of the obtainedsuperhydrophobic surfaces with different structures under condensation.The results show that the wettability decrease of setcreasea purpurea leafsurface is the least under condensation, which indicates superhydrophobicsurface with smaller hierarchical structure is more capable to keep waterrepellency under condensation.(4) A simple and novel method was applied to obtain aPDMS/CaCO3coating, and then sparing the coating onto substrates underhigh pressure, after the coating was dried, a superhydrophobic coatingwith micro-and nano-hierarchical structure was obtained. Condensationtest showed that the wettability of obtained PDMS/CaCO3coating surfacegreatly changed under condensation, and the possible reason which maylead to the decrease of water repellency of the obtained superhydrophobicPDMS/CaCO3coating is analyzed.(5) A bamboo leaf-like superhydrophobic hierarchical structure wasobtained on iron surface by combining template method and corrosionmethod. Then the obtained iron surface was modified by stearic acid tomake the surface structure more similar to the micro-and nano-hierarchical structure of bamboo leaf. After modified by stearic acid, theobtained iron surface became superhydrophobic.