Yang Zhen, Tian Yanling, Zhao Yuechao, Yang Chengjuan
Key Laboratory of Mechanism Theory & Equipment Design, Ministry of education, Tianjin University, Tianjin 300350, China.
School of Engineering, University of Warwick, Coventry CV4 7AL, UK.
Materials (Basel). 2019 Jan 16;12(2):278. doi: 10.3390/ma12020278.
Nanosecond laser ablated metallic surfaces showed initial super-hydrophilicity, and then experienced gradual wettability conversion to super-hydrophobicity with the increase of exposing time to ambient air. Due to the presence of hierarchical structures and change of surface chemistry, the laser-induced Inconel alloy surfaces showed a stable apparent contact angle beyond 150° over 30-day air exposure. The wetting states were proposed to elucidate the initial super-hydrophilicity and the final super-hydrophobicity. The basic fundaments behind the wettability conversion was explored by analyzing surface chemistry using X-ray photoelectron spectroscopy (XPS). The results indicated that the origins of super-hydrophobicity were identified as the increase of carbon content and the dominance of C⁻C(H) functional group. The C⁻C(H) bond with excellent nonpolarity derived from the chemisorbed airborne hydrocarbons, which resulted in dramatic reduction of surface-free-energy. This study confirmed that the surface chemistry is not the only factor to determine surface super-hydrophobicity. The laser-induced super-hydrophobicity was attributed to the synergistic effect of surface topography and surface chemical compositions. In this work, the corresponding chemical reaction was particularly described to discuss how the airborne hydrocarbons were attached onto the laser ablated surfaces, which reveals the generation mechanism of air-exposed super-hydrophobic surfaces.
纳秒激光烧蚀的金属表面呈现出初始的超亲水性，随后随着暴露于环境空气中的时间增加，逐渐经历润湿性转变为超疏水性。由于存在分级结构和表面化学性质的变化，激光诱导的因科镍合金表面在暴露于空气中30天的时间里，表现出超过150°的稳定表观接触角。提出了润湿状态来解释初始的超亲水性和最终的超疏水性。通过使用X射线光电子能谱（XPS）分析表面化学性质，探索了润湿性转变背后的基本原理。结果表明，超疏水性的起源被确定为碳含量的增加和C⁻C(H)官能团的主导地位。源自化学吸附的空气中碳氢化合物的具有优异非极性的C⁻C(H)键，导致表面自由能显著降低。这项研究证实，表面化学性质不是决定表面超疏水性的唯一因素。激光诱导的超疏水性归因于表面形貌和表面化学成分的协同作用。在这项工作中，特别描述了相应的化学反应，以讨论空气中的碳氢化合物如何附着在激光烧蚀表面上，这揭示了暴露于空气中的超疏水表面的生成机制。
