Yale University, New Haven, Connecticut 06520, USA.
Nat Commun. 2013;4:2728. doi: 10.1038/ncomms3728.
The Johnson-Kendall-Roberts theory is the basis of modern contact mechanics. It describes how two deformable objects adhere together, driven by adhesion energy and opposed by elasticity. Here we characterize the indentation of glass particles into soft, silicone substrates using confocal microscopy. We show that, whereas the Johnson-Kendall-Roberts theory holds for particles larger than a critical, elastocapillary lengthscale, it fails for smaller particles. Instead, adhesion of small particles mimics the adsorption of particles at a fluid interface, with a size-independent contact angle between the undeformed surface and the particle given by a generalized version of the Young's law. A simple theory quantitatively captures this behaviour and explains how solid surface tension dominates elasticity for small-scale indentation of soft materials.
约翰逊-肯德尔-罗伯茨理论是现代接触力学的基础。它描述了两个可变形物体如何在粘附能的驱动下结合在一起，并受到弹性的阻碍。在这里，我们使用共聚焦显微镜来描述玻璃颗粒压入软质硅酮基底的情况。我们表明，尽管约翰逊-肯德尔-罗伯茨理论适用于大于临界弹性毛细长度尺度的颗粒，但对于较小的颗粒则不适用。相反，小颗粒的粘附类似于在流体界面上的颗粒吸附，未变形表面与颗粒之间的接触角与广义的杨定律一致，与颗粒大小无关。一个简单的理论可以定量地捕捉这种行为，并解释了在软材料的小尺度压痕中，固体表面张力如何支配弹性。
