Department of Physics, National University of Singapore, Singapore 117551.
Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, Singapore 117557.
Proc Natl Acad Sci U S A. 2021 Sep 21;118(38). doi: 10.1073/pnas.2108074118.
The spreading of a liquid droplet on flat surfaces is a well-understood phenomenon, but little is known about how liquids spread on a rough surface. When the surface roughness is of the nanoscopic length scale, the capillary forces dominate and the liquid droplet spreads by wetting the nanoscale textures that act as capillaries. Here, using a combination of advanced nanofabrication and liquid-phase transmission electron microscopy, we image the wetting of a surface patterned with a dense array of nanopillars of varying heights. Our real-time, high-speed observations reveal that water wets the surface in two stages: 1) an ultrathin precursor water film forms on the surface, and then 2) the capillary action by nanopillars pulls the water, increasing the overall thickness of water film. These direct nanoscale observations capture the previously elusive precursor film, which is a critical intermediate step in wetting of rough surfaces.
液滴在平坦表面上的铺展是一种被充分理解的现象，但对于液体在粗糙表面上的铺展方式却知之甚少。当表面粗糙度处于纳米尺度时，毛细力起主导作用，液体通过润湿纳米级纹理（这些纹理充当毛细管）来铺展。在这里，我们采用先进的纳米制造技术和液相透射电子显微镜相结合的方法，对具有不同高度的纳米柱密集阵列图案化表面的润湿过程进行成像。我们的实时、高速观测揭示，水在两个阶段润湿表面：1）在表面上形成超薄膜状的预前水膜，然后 2）纳米柱的毛细作用拉动水，增加水膜的整体厚度。这些直接的纳米级观测捕捉到了之前难以捉摸的预前膜，这是粗糙表面润湿的一个关键中间步骤。
