Division of Molecular and Materials Simulation, Key Laboratory for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029, China.
J Chem Phys. 2011 Mar 28;134(12):124704. doi: 10.1063/1.3570657.
Capillary bridge is a common phenomenon in nature and can significantly contribute to the adhesion of biological and artificial micro- and nanoscale objects. Especially, it plays a crucial role in the operation of atomic force microscopy (AFM) and influences in the measured force. In the present work, we study the rupture kinetics and transition pathways of liquid bridges connecting an AFM tip and a flat substrate during a process of pulling the tip off. Depending on thermodynamic conditions and the tip velocity, two regimes corresponding to different transition pathways are identified. In the single-bridge regime, the initial equilibrium bridge persists as a single one during the pulling process until the liquid bridge breaks. While, in the multibridge regime the stretched liquid bridge transforms into an intermediate state with a collection of slender liquid bridges, which then break gradually during the pulling process. Moreover, the critical rupture distance at which the bridges break changes with the tip velocity and thermodynamic conditions, and its maximum value occurs near the boundary between the single-bridge regime and the multibridge regime, where the longest range capillary force is produced. In this work, the effects of tip velocity, tip size, tip-fluid interaction, and humidity on rupture kinetics and transition pathways are also systematically studied.
毛细桥是自然界中常见的现象，它对生物和人工微纳尺度物体的粘附有重要贡献。特别是，它在原子力显微镜（AFM）的操作中起着关键作用，并影响测量力。在本工作中，我们研究了在针尖脱离过程中连接 AFM 针尖和平面基底的液体桥的断裂动力学和转变途径。根据热力学条件和针尖速度，确定了对应于不同转变途径的两个区域。在单桥区域中，初始平衡桥在拉伸过程中保持为单个桥，直到液体桥断裂。而在多桥区域中，拉伸的液体桥转变为中间状态，其中包含一系列细长的液体桥，然后在拉伸过程中逐渐断裂。此外，桥断裂的临界断裂距离随针尖速度和热力学条件而变化，其最大值出现在单桥区域和多桥区域的边界附近，此处产生最长程的毛细力。在这项工作中，还系统地研究了针尖速度、针尖尺寸、针尖-流体相互作用和湿度对断裂动力学和转变途径的影响。
