College of Aerospace Engineering, Chongqing University, Chongqing, 400044, China.
Soft Matter. 2017 Sep 13;13(35):6011-6020. doi: 10.1039/c7sm01013c.
Controlling the morphologies and properties of the surface and/or interface of bimaterials consisting of soft polymers provides new opportunities in many engineering applications. Crease is a widely observed deformation mode in nature and engineering applications for soft polymers where the smooth surface folds into a region of self-contact with a sharp tip, usually induced by the instability from mechanical compression or swelling. In this work, we explore the competition mechanisms between surface and interface creases through numerical simulations and experimental studies on bilayer hydrogels. The surface or interface crease of the bilayer hydrogels under swelling is governed by both the modulus ratio (M/M) and the height ratio (H/H). Through extensive numerical simulations, we find that the interface crease of the bilayer hydrogels can only occur at a moderate modulus ratio (24 < M/M < 96) and a large height ratio (H/H ≥ 8). Guided by this phase diagram, our experiments confirm that both surface and interface creases can be generated by swelling triggered instability, and the transition of surface to interface creases occurs at the critical value of the height ratio (H/H) between 5 and 10. Such an observation is in good agreement with our numerical predictions. Fundamental understandings on the switching between the surface and interface creases provide new insights into the design of highly tunable soft materials and devices over a wide range of length scales.
控制由软聚合物组成的双材料的表面和/或界面的形态和特性为许多工程应用提供了新的机会。褶皱是软聚合物在自然和工程应用中广泛观察到的一种变形模式，其中光滑的表面折叠成一个自接触区域，通常由机械压缩或膨胀引起的不稳定性引起。在这项工作中，我们通过数值模拟和双层水凝胶的实验研究来探索表面和界面褶皱之间的竞争机制。双层水凝胶在溶胀下的表面或界面褶皱由模量比（M/M）和高度比（H/H）共同控制。通过广泛的数值模拟，我们发现双层水凝胶的界面褶皱只能在中等模量比（24< M/M <96）和大高度比（H/H≥8）下发生。通过这个相图的指导，我们的实验证实了表面和界面褶皱都可以通过溶胀触发的不稳定性产生，并且表面到界面褶皱的转变发生在高度比（H/H）为 5 到 10 之间的临界值处。这种观察结果与我们的数值预测非常吻合。对表面和界面褶皱之间的转换的基本理解为在广泛的长度尺度上设计高度可调的软材料和器件提供了新的见解。
