Yu Senjiang, Sun Yadong, Zhang Xiaofei, Lu Chenxi, Zhou Hong, Ni Yong
Innovative Center for Advanced Materials (ICAM), Hangzhou Dianzi University, Hangzhou 310012, People's Republic of China.
Department of Physics, China Jiliang University, Hangzhou 310018, People's Republic of China.
Phys Rev E. 2019 Jun;99(6-1):062802. doi: 10.1103/PhysRevE.99.062802.
Fascinating crack and wrinkle patterns driven by stresses are ubiquitous in natural and artificial systems. It is of great interest to control the morphologies of stress-driven patterns by using facile techniques. Here we report on the spontaneous formation of hierarchical wrinkles and oscillatory cracks in metal films deposited on liquid (or soft polymer) stripes. It is found that the metal film is under a tensile stress during deposition owing to the thermal expansion of the liquid substrate. As the film thickness is beyond a critical value, oscillatory cracks with sawtoothlike shapes form on the liquid stripes. The ratio of crack oscillation period to amplitude is independent of the stripe width and film material, which can be well explained by the "brittle adhesive joints" model. After deposition, the metal film is under a compressive stress, which is relieved by formation of various wrinkle patterns. Hierarchical wrinkles with changing wavelengths form near the stripe edge while labyrinth or wavy wrinkles form at the center. Energy analysis was adopted to explain the formation and evolution of the wrinkle patterns. This study could promote better understanding of the formations of crack and wrinkle patterns in constrained film structures and controllable fabrication of stress-driven patterns by prefabricating liquid (or soft polymer) interlayer arrays.
由应力驱动产生的迷人裂纹和皱纹图案在自然和人工系统中无处不在。利用简便技术来控制应力驱动图案的形态具有极大的研究价值。在此，我们报道了在沉积于液体（或软聚合物）条纹上的金属薄膜中自发形成的分层皱纹和振荡裂纹。研究发现，由于液体基底的热膨胀，金属薄膜在沉积过程中处于拉伸应力状态。当薄膜厚度超过临界值时，在液体条纹上会形成锯齿状的振荡裂纹。裂纹振荡周期与振幅的比值与条纹宽度和薄膜材料无关，这可以通过“脆性粘结接头”模型得到很好的解释。沉积后，金属薄膜处于压缩应力状态，通过形成各种皱纹图案来释放该应力。在条纹边缘附近会形成波长不断变化的分层皱纹，而在中心则会形成迷宫状或波浪状皱纹。采用能量分析来解释皱纹图案的形成和演变。这项研究有助于更好地理解受限薄膜结构中裂纹和皱纹图案的形成，以及通过预制液体（或软聚合物）夹层阵列对应力驱动图案进行可控制造。
