Instituto de Microelectrónica de Madrid CNM-CSIC, Isaac Newton 8, PTM, 28760 Tres Cantos, Madrid, Spain.
Small. 2010 Dec 6;6(23):2725-30. doi: 10.1002/smll.201001297.
The sticking effect between hydrophilic surfaces occurring at increasing relative humidity (RH) is an everyday phenomenon with uncountable implications. Here experimental evidence is presented for a counterintuitive monotonous decrease of the capillary adhesion forces between hydrophilic surfaces with increasing RH for the whole humidity range. It is shown that this unexpected result is related to the actual shape of the asperity at the nanometer scale: a model based on macroscopic thermodynamics predicts this decrease in the adhesion force for a sharp object ending in an almost flat nanometer-sized apex, in full agreement with experiments. This anomalous decrease is due to the fact that a significant growth of the liquid meniscus formed at the contact region with increasing humidity is hindered for this geometry. These results are relevant in the analysis of the dynamical behavior of nanomenisci. They could also have an outstanding value in technological applications, since the undesirable sticking effect between surfaces occurring at increasing RH could be avoided by controlling the shape of the surface asperities at the nanometric scale.
在相对湿度（RH）增加时，亲水表面之间发生的黏附现象是一种无处不在的日常现象，具有无数的影响。本文提供了实验证据，表明在整个湿度范围内，亲水表面之间的毛细黏附力会随着 RH 的增加而呈反直觉的单调下降。结果表明，这种出乎意料的结果与纳米尺度上的实际凸起形状有关：基于宏观热力学的模型预测，对于以几乎平坦的纳米级尖端结束的尖锐物体，黏附力会随着 RH 的增加而减小，这与实验结果完全一致。这种反常的减小是由于在接触区域形成的液体弯月面随着湿度的增加而显著增大，而对于这种几何形状，这种增大受到阻碍。这些结果对于分析纳米弯月面的动力学行为具有重要意义。它们在技术应用中也可能具有突出的价值，因为通过控制纳米尺度表面凸起的形状，可以避免 RH 增加时表面之间发生的不希望的黏附效应。
