Song Qingrui, Liu Kun, Sun Wei, Chen Rongxin, Ji Jiawei, Jiao Yunlong, Gao Tianyan, Ye Jiaxin
Institute of Tribology School of Mechanical Engineering, Hefei University of Technology, Hefei, Anhui 230009, China.
Langmuir. 2021 Oct 12;37(40):11737-11749. doi: 10.1021/acs.langmuir.1c01635. Epub 2021 Oct 1.
Capillary forces of a shearing liquid bridge can significantly affect the friction and adhesion of interacting surfaces, but the underlying mechanisms remain unclear. We custom built a surface force apparatus (SFA, ±2 μN) equipped with optical microscopy and performed normal and lateral force measurements on a reciprocating water bridge formed between two flat plates. A modified wedge method was developed to correct the unique force measurement errors caused by the changing bridge geometry and position. The results found (1) strong linear relations among the bridge shear displacement, the cosine difference between the left and right contact angles, and the lateral adhesion force and (2) the normal adhesion force increased monotonically up to 13% as the bridge geometry approached its axisymmetric state. Quasi-static force analyses based on a newly developed decahedral model showed good agreement with the experiments and improved accuracy compared with that of cylindrical or rectangular column models previously proposed in the literature. Although limited in certain aspects, this study may (1) prove helpful to the design and analysis of liquid bridge force experiments on platforms similar to the SFA used in this study and (2) help to bridge the gap between friction and liquid bridge physics in the literature.
剪切液桥的毛细作用力会显著影响相互作用表面的摩擦力和粘附力，但其潜在机制仍不清楚。我们定制了一台配备光学显微镜的表面力仪（SFA，精度±2 μN），并对两块平板之间形成的往复水桥进行了法向力和侧向力测量。开发了一种改进的楔形方法来校正由桥几何形状和位置变化引起的独特力测量误差。结果发现：（1）桥的剪切位移、左右接触角的余弦差和侧向粘附力之间存在很强的线性关系；（2）随着桥几何形状接近其轴对称状态，法向粘附力单调增加，最高可达13%。基于新开发的十面体模型的准静态力分析与实验结果吻合良好，与文献中先前提出的圆柱或矩形柱模型相比，精度有所提高。尽管本研究在某些方面存在局限性，但它可能（1）有助于设计和分析与本研究中使用的SFA类似平台上的液桥力实验，（2）有助于弥合文献中摩擦力和液桥物理之间的差距。
