| 摘要: |
| 液滴撞击固体表面是自然界的常见现象，研究超疏水表面的液滴撞击对其润湿性的影响，对于超疏水性材料的潜在应用具有重要的科学意义。采用 3、10、20 min 氧等离子体处理（OPT）和 1 min 八氟环丁烷等离子体聚合沉积（PPD）的等离子体方法改性聚四氟乙烯（PTFE）表面，获得具有不同尺寸和间距的微 / 纳米锥的超疏水 PTFE 表面，研究射频等离子体改性 PTFE 表面的液滴静态接触角、滚动角及液滴撞击动力学行为，分析在不同个数液滴撞击后 PTFE 表面的润湿性和液滴撞击行为变化，确定 PTFE 表面液滴撞击起电效应的影响机制。结果表明：通过 1~9 个液滴撞击后，PTFE 表面的静态接触角随撞击液滴数量增加而减小，导致静态接触角低于 150°；液滴滚动角随撞击液滴数量增加而增大，造成液滴滚动角高于 10°。 撞击液滴的接触时间随撞击液滴数量增加而增大，回弹系数随撞击液滴数量增加而减小。随撞击液滴数量增加，回弹液滴的正电荷和 PTFE 表面的负电压增大，PTFE 表面的负电荷对液滴产生强吸引作用，导致低粘附超疏水性被破坏。3 min OPT 和 1 min PPD 改性 PTFE 表面的纳米锥间距小，密度大，表面负电荷量增加明显，造成 PTFE 表面的疏水性降低的程度最显著。 研究结果可为改善超疏水稳定性的表面织构设计提供理论依据。 |
| 关键词: 超疏水性表面 液滴撞击 接触起电 聚四氟乙烯(PTFE) 接触角 |
| DOI：10.11933/j.issn.1007-9289.20230106002 |
| 分类号:TG156；TB114 |
| 基金项目:国家自然科学基金（51975086, 52111530043, U21B2078）；中央高校基本科研业务费（DUT22LAB107）资助项目 |
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| Effect of Contact Electrification During Water Droplet Impact on the Wettability of PTFE Surfaces Modified by Radio Frequency Plasma |
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LI Yupeng1, MENG Xiangren1, LIU Yuxia1, HUO Lei1, LEI Mingkai1, STARINSKIY Sergey V2, TEREKHOV Vladimir2
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1.School of Materials Science and Engineering, Dalian University of Technology,Dalian 116024 , China;2.Kutateladze Institute of Thermophysics, Siberian Branch of Russian Academy of Sciences,Novosibirsk 630090 , Russia
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| Abstract: |
| A water droplet impacting a solid surface is a natural universal phenomenon. The impact behavior of water droplets and their effect on the superhydrophobicity of anti-wetting surfaces are important for the practical application of anti-wetting materials. In this study, radio frequency plasma modification methods including oxygen plasma treatment (OPT) and octafluorocyclobutane (C4F8) plasma polymerization deposition (PPD) are used to fabricate superhydrophobic surfaces on polytetrafluoroethylene (PTFE) substrates. Micro / nanocone arrays with different heights and spacing distances and fluorocarbon films with a low surface energy are fabricated on superhydrophobic PTFE surfaces by OPT for 3, 10, and 20 min, and PPD for 1 min. The height and distance of the cone structure on the PTFE surfaces increase as the OPT duration increases. The transition from a nanocone to a microcone array is achieved on the PTFE surfaces when the OPT duration is increases to 10 min. Complete droplet rebound behavior is achieved on superhydrophobic PTFE surfaces with a micro / nanocone array. The water contact angle increases, and the rolling angle decreases on the superhydrophobic PTFE surfaces as the OPT duration increases. Superhydrophobic surfaces with microcones having a wide spacing distance and low array density preserve a low adhesive force on water droplets under static conditions. The contact time increases and the restitution coefficient decreases when the water droplet impactes the superhydrophobic surfaces with an increased OPT duration. Superhydrophobic PTFE surfaces with nanocones having a low spacing distance and high array density exhibit a low adhesive force to the water droplet during droplet impact. Changes in the wettability and impacting behaviors of the water droplets are investigated after water droplet impact by changing the number of impacting droplets. The contact electrification on the PTFE surfaces with micro / nanocone arrays at different heights and spacing distances is analyzed by measuring the accumulated potentials of the PTFE surfaces and accumulated charge quantity of the impacting droplets. The water contact angle decreases and the rolling angle on the PTFE surfaces increases as the number of impacting droplets increases up to nine. A water contact angle of lower than 150°and rolling angle of lower than 10°are observed on the PTFE surfaces with the micro / nanocone array after the water droplet impactes with droplet number nine. The contact time of the impacting water droplet increases and its restitution coefficient decreases as the number of impacting droplets increases. The accumulated potentials of the PTFE surfaces and charge quantity of the impacting droplets increase. The attractive force of the accumulated negative charges on the water droplets resultes in the damage of superhydrophobicity on the PTFE surfaces and a change in the water droplet impacting behaviors. The PTFE surfaces fabricated by OPT for 3 min and PPD for 1 min preserve the nanocones at a low spacing distance and high array density. The PTFE surfaces with nanocones having a high array density preserve the highly accumulated negative charges after the water droplet impact under the increased number of impacting droplets. The high surface potential causes a remarkable increase in the wettability of the PTFE surfaces as well as a change in the contact time and restitution coefficient of the impacting water droplets. The accumulated negative charge and surface potential of the PTFE surfaces with the microcones having a wide spacing distance and low array density by OPT for 20 min and PPD for 1 min are low after droplet impact under the increased number of impacting droplets. The influence of the droplets on the wettability of the PTFE surfaces and the changes in the contact time and restitution coefficient of the impacting water droplets are weakened. In conclusion, this study demonstrates the effect of contact electrification on the superhydrophobic stability of surfaces with different textures under water droplet impact. |
| Key words: superhydrophobic surface water droplet impacting contact electrification polytetrafluoroethylene(PTFE) contact angle |
