The instability behavior of a compressive bilayer on a soft substrate is of significance for epidermal electronics adhered to human skin. Conventionally, two different wrinkling modes dependent of the modulus of intermediate layer were proposed to evolve from flat feature. Here, we uncover a new periodic pattern of secondary wrinkling feature with further compression in the case of a moderate-modulus intermediate layer. FEM simulation results illustrate a linear relationship between this wavelength of secondary wrinkling and the modulus of intermediate layer. An analytical model based on Timoshenko beam theory is utilized to predict the wavelength and critical strain of this secondary wrinkling, which agrees well with that in FEM simulations. Further, a phase diagram of instability feature in the system of bilayer/soft substrate is proposed. The secondary wrinkling feature with such large wavelength has broad applications in tunable surface morphologies for smart glasses, color controlling and manipulation of water droplets.

对于粘附在人体皮肤上的表皮电子设备，软质基底上的压缩双层的不稳定性行为具有重要意义。常规地，提出了两种取决于中间层的模量的起皱模式以从平坦特征演变。在这里，我们在中等模量中间层的情况下，通过进一步压缩发现了二次起皱特征的新周期性模式。有限元模拟结果表明，二次起皱的波长与中间层的模量之间存在线性关系。利用基于Timoshenko束理论的分析模型来预测该二次起皱的波长和临界应变，这与FEM仿真中的结果非常吻合。此外，提出了一种双层/软衬底系统中的不稳定性特征的相图。