Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2013 Jul 30;110(31):12545-8. doi: 10.1073/pnas.1302269110. Epub 2013 Jul 15.
Thin soft elastic layers serving as joints between relatively rigid bodies may function as sealants, thermal, electrical, or mechanical insulators, bearings, or adhesives. When such a joint is stressed, even though perfect adhesion is maintained, the exposed free meniscus in the thin elastic layer becomes unstable, leading to the formation of spatially periodic digits of air that invade the elastic layer, reminiscent of viscous fingering in a thin fluid layer. However, the elastic instability is reversible and rate-independent, disappearing when the joint is unstressed. We use theory, experiments, and numerical simulations to show that the transition to the digital state is sudden (first-order), the wavelength and amplitude of the fingers are proportional to the thickness of the elastic layer, and the required separation to trigger the instability is inversely proportional to the in-plane dimension of the layer. Our study reveals the energetic origin of this instability and has implications for the strength of polymeric adhesives; it also suggests a method for patterning thin films reversibly with any arrangement of localized fingers in a digital elastic memory, which we confirm experimentally.
作为相对刚性体之间的连接的薄软弹性层可作为密封剂、热绝缘体、电绝缘体、机械绝缘体、轴承或粘合剂。当这种接头受到应力时，即使保持完全粘附，薄弹性层中的暴露自由弯月面也会变得不稳定，导致空间周期性的空气指状物侵入弹性层，使人联想到薄流体层中的粘性指状物。然而，弹性不稳定性是可逆的且与速率无关，当接头不受应力时，不稳定性就会消失。我们使用理论、实验和数值模拟表明，向数字状态的转变是突然的（一级），指状物的波长和幅度与弹性层的厚度成正比，而引发不稳定性所需的分离与层的平面尺寸成反比。我们的研究揭示了这种不稳定性的能量起源，对聚合物粘合剂的强度有影响；它还提出了一种方法，可通过在数字弹性存储器中以任何局部指状物的布置来对薄膜进行可逆图案化，我们通过实验证实了这一点。
