Effect of nano structures on the nucleus wetting modes during water vapour condensation: from individual groove to nano-array surface
Effect of nano structures on the nucleus wetting modes during water vapour condensation: from individual groove to nano-array surface
复制标题
纳米结构对水蒸气凝结过程中核润湿模式的影响：从单个凹槽到纳米阵列表面
DOI：
10.1039/c5ra23836f
复制
发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Ma X. H.
中科院分区：
文献类型：
--
作者：
Xu W.;Lan Z.;Peng B. L.;Wen R. F.;Ma X. H.
表面的几何结构对水蒸气凝结过程中核的形成和生长及其传热传质性能有重要影响。在本研究中，通过分子动力学模拟研究了单个凹槽和纳米阵列表面的核润湿模式。研究结果提出了v型槽核润湿模式由内征接触角θ和横截角β决定的判据。当截面角减小到β < 2θ−π时，原子核可以悬浮在凹槽中心，悬浮高度随β的减小而增大。对于纳米阵列表面，由于初始核非常小，且核表面波动频繁，在初始成核阶段，核可以湿润相邻纳米阵列之间的凹槽。在β < 2θ−π的表面上，随着成核的持续，润湿模式会发生变化，核可以离开槽底形成Cassie型核。随着润湿模式的转变，核的视接触角也急剧增大。此外，在满足条件的纳米阵列超疏水表面上，还观察了成核液滴的动力学行为。该表面上的液滴聚结后可以恢复球形，并发生液滴跳跃，表明表面粘性较低。研究结果揭示了原子核与几何结构之间的界面现象，并为构建Cassie模式原子核的纳米阵列表面提供了指导。
The geometrical structures of surfaces are important to the formation and growth of nuclei during water vapor condensation and the related heat and mass transfer performances. In the present research, the nucleus wetting modes on individual grooves and nano-array surfaces were investigated by molecules dynamics simulations. The results proposed a criterion that the nucleus wetting modes on a V-shaped groove are determined by the intrinsic contact angle θ and the cross sectional angle β. As the cross sectional angle decreases to β < 2θ − π, the nuclei can suspend in the groove center and the suspending height increases with decreasing β. For the nano-array surfaces, the nucleus can wet the grooves between adjacent nano arrays during the initial nucleation stage as the initial nuclei are very small and the nucleus surface are fluctuating frequently. The wetting mode may change as nucleation continuous and the nucleus can depart from the groove bottom to form a Cassie mode nucleus on a surface with β < 2θ − π. The apparent contact angle of nucleus also increases sharply with the wetting mode transition. Moreover, the dynamic behaviors of nucleating droplets were also observed on a nano-array superhydrophobic surface that meets the criterion. The droplets on this surface can recover the spherical shape after coalescence and the droplet jumping occurs, indicating a lower surface stiction. The results provide an insight of the interfacial phenomenon between the nucleus and the geometrical structures and propose a guideline to construct nano-array surfaces in the aim of promoting the Cassie mode nucleus.