随着微纳加工技术的迅速发展, 在固体表面制备微柱阵列逐渐成为调控液体输运方向和速率的重要手段. 微柱阵列表面的润湿在能源、环境、健康、航天等领域表现出巨大的应用价值, 受到了工业界的广泛关注. 微柱阵列的固-液界面问题是一个典型的多尺度流固耦合问题. 微柱阵列为固-液界面引入了新的时空尺度和非常复杂的竞争机制, 因此引起了学术界的极大兴趣. 液体的输运方向和速率分别与接触线的对称性和润湿动力学密切相关. 本文采用跨尺度润湿实验和表界面物理力学相结合的研究方法, 围绕移动接触线对称性和润湿动力学两个重要学术问题, 针对亲液的微柱阵列表面液滴润湿铺展中存在的三个关键科学问题: 单个微柱对前进接触线的钉扎作用、微柱阵列表面液滴的动态润湿和微柱阵列的构形对润湿的影响, 开展研究工作.

单个微柱对前进接触线的钉扎作用: 在固体表面制备单个微柱, 实验上发现了在相同微柱和液体条件下, 前进接触线被单个微柱钉扎的作用表现为促进和抑制接触线移动的两种模式; 揭示了接触线遇到微柱的相互作用过程, 包括内角润湿、液膜沿微柱爬升和横向扩展; 通过进一步的实验发现了决定前进接触线的移动被单个微柱促进或抑制的物理量为接触线前端液膜倾角, 并且发现随着单个微柱的尺寸的增大, 液膜倾角的临界值也增大.

微柱阵列表面液滴的动态润湿: 液滴铺展过程出现了双层液膜结构, 并且液滴接触线发生对称性破缺; 揭示了微柱阵列带来的过剩驱动力与液体的表面张力的竞争机制, 阐明了微柱阵列的特征参数、液体的表面张力、液体的黏性对接触线对称性影响; 使用从分子尺度出发的统计力学方法——分子动理论, 得到了润湿的物理机理与动力学标度关系; 润湿实验证实了润湿面积与时间的标度关系; 相应动力学标度指数大于光滑表面液滴铺展的标度指数, 表明了亲液微柱阵列表面可显著加速液体的铺展.

微柱阵列的构形对润湿的影响: 采用二维准晶的微柱阵列表面, 提出了微柱阵列的构形熵, 获得了五重对称的接触线; 发现了准晶微柱阵列的构形使接触线不仅发生对称性破缺, 还伴随着对称性的自发转变; 通过量纲分析, 结合系统的润湿实验, 给出了接触线对称性破缺与自发转变的机制; 结合准晶微柱阵列短程无序长程有序的性质, 分析了液滴铺展过程的驱动和耗散作用, 获得了准晶微柱阵列表面液滴铺展的标度律; 揭示了不同构形的微柱阵列对液滴铺展动力学标度指数的作用.

本论文系统地研究了亲液微柱阵列表面对液滴润湿的作用, 厘清了接触线的对称性与润湿动力学规律及相关物理机理, 为通过合理设计表面微结构, 实现控制液体的输运方向和速率的相关应用提供了理论指导.

With the development of micro- and nano-fabrication technology, the method of fabricating microstructures on a solid surface has become significant in controlling the direction and speed of liquid transport. Wetting on a micro pillar-arrayed surface, which exhibits brilliant value in a broad range of fields such as energy, environment, health and aerospace, has drawn widespread attention in industry. The pillar-arrayed solid-liquid interface is an issue of multi-scale fluid structure interaction. The micropillars induced new temporal and spatial scales and complex competition to the solid-liquid interface. As a result, this issue has attracted considerable interests in academia. The direction and speed of liquid transport are closely related to the symmetry breaking of contact lines and wetting dynamics, respectively. Adopting multiscale wetting experiments and physical mechanics of surfaces and interfaces, concerning two crucial problems, i.e. the symmetry of contact lines and wetting dynamics, this dissertation studied three key scientific issues: the pinning effects of a single micro-pillar on an advancing contact line, dynamic wetting of a droplet on a pillar-arrayed surface, and the effects of the configuration of pillar arrays on wetting.

The pinning effects of a single micro-pillar on an advancing contact line: Fabricating a single micro-pillar on a solid surface, the experimental results showed that with fixed pillar-liquid pair the pinning effects have two distinct regimes, that is, the advancing contact line being assisted and resisted by a single micro-pillar; the interaction between the advancing contact line and a single pillar was revealed, and this interaction includes interior corner flow, liquid film climbing up along the pillar and liquid film spreading; further experiments showed that the dip angle of the liquid front is the key physical factor in determining whether the contact line is resisted or assisted by a single micro-pillar; and the threshold of the dip angle of liquid front increases with the size of single micro-pillar.

Dynamic wetting of a droplet on a pillar-arrayed surface: A bilayer structure of a droplet and symmetry breaking of the contact line appeared in the spreading process; the competition between excess driving force induced by micropillars and liquid surface tension was revealed, the effects of pillar parameters, surface tension and liquid viscosity on the symmetry of a contact line were given; adopting the molecular kinetic theory, which is from molecular scale and based on the method of statistical mechanics, the physical mechanism and a scaling law of the wetting dynamics were obtained; the scaling law was found to agree with the experimental results; the exponent of the scaling law was found larger than that on a smooth flat surface, indicating that periodically pillar-arrayed surface significantly accelerated the spreading of a droplet.

The effects of the configuration of pillar arrays on wetting: Employing a pillar-arrayed surface with 2-dimensional quasicrystal arrangement, the configurational entropy of the pillar array was calculated, and a contact line with five-fold symmetry was obtained; the symmetry of a contact line was found to breaking and spontaneous transforming; adopting dimensional analysis and systematic experiments, the symmetry transition of the contact line was analyzed; considering the short-range disorder and long-range order surface, the driving and dissipation energy during the spreading process were analyzed, and the scaling law of the pillar-arrayed surface with 2-dimensional quasicrystal arrangement was derived; the effects of the configuration of pillar-arrayed surfaces on wetting dynamics were revealed.

In this dissertation, the effects of a lyophilic pillar-arrayed surface on liquid spreading were systematically explored. The physical mechanisms of the symmetry of contact line and the dynamics during spreading were revealed. This study can provide theoretical guidance for designing structures of solid surfaces to control the flowing direction and speed of liquid in applications.