Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany.
Physics of Fluids Group, Mesa+ Institute, University of Twente, 7500 AE Enschede, Netherlands.
Phys Rev Lett. 2021 Jul 9;127(2):028001. doi: 10.1103/PhysRevLett.127.028001.
The compression of soft elastic matter and biological tissue can lead to creasing, an instability where a surface folds sharply into periodic self-contacts. Intriguingly, the unfolding of the surface upon releasing the strain is usually not perfect: small scars remain that serve as nuclei for creases during repeated compressions. Here we present creasing experiments with sticky polymer surfaces, using confocal microscopy, which resolve the contact line region where folding and unfolding occurs. It is found that surface tension induces a second fold, at the edge of the self-contact, which leads to a singular elastic stress and self-similar crease morphologies. However, these profiles exhibit an intrinsic folding-unfolding asymmetry that is caused by contact line pinning, in a way that resembles wetting of liquids on imperfect solids. Contact line pinning is therefore a key element of creasing: it inhibits complete unfolding and gives soft surfaces a folding memory.
软弹性物质和生物组织的压缩会导致起皱，这是一种表面急剧折叠成周期性自接触的不稳定性。有趣的是，在释放应变时，表面的展开通常并不完美：小的疤痕仍然存在，这些疤痕在反复压缩时充当起皱的核。在这里，我们使用共聚焦显微镜展示了粘性聚合物表面的起皱实验，该实验可以解析发生折叠和展开的接触线区域。结果发现，表面张力会在自接触的边缘诱导出第二个折叠，从而导致奇异的弹性应力和自相似的起皱形态。然而，这些轮廓表现出一种内在的折叠-展开不对称性，这是由接触线钉扎引起的，这种方式类似于液体在不完美固体上的润湿。因此，接触线钉扎是起皱的关键因素：它抑制了完全展开，并使软表面具有折叠记忆。
