Wrinkling of Interfacial Layers in Stratified Composites

O DOI: 10.1002/adem.201200387 M M U Wrinkling of Interfacial Layers in Stratified Composites** N IC By Yaning Li,y Narges Kaynia,y Stephan Rudykh and Mary C. Boyce* A T IO N Many structured composites in nature possess undulating and wrinkled interfacial layers that regulate mechanical, chemical, acoustic, adhesive, thermal, electrical, and optical functions, and also serve to reveal underlying physiological mechanisms in the diagnosis of diseases. As one example, the wavy layers of the silvery reflectors around the eyes of squid (L. Pealeii) facilitate broadband reflectance and result in silvery iridescence, providing inspiration for creating composite structures with different optical functions. Another example is the wavy elastica lamellae embedded in soft muscle in arterial walls which provides a diagnostic signature for disease. The degree of the elastica lamellae undulation was found to be significantly greater in persons with coronary artery disease compared to that found in the non-coronary disease group. Hence, understanding the mechanism governing the waveform formation can provide clues to other underlying structural, bio-chemical and mechanical changes. Furthermore, the ability to actively alter the interface structure can enable on-demand tunability of these attributes and functions to provide, for example, active control of wave propagation phenomenon (e.g., phononic and photonic), mechanical stiffness and deformation, and material swelling and growth. In this investigation, we explore the mechanisms of the formation of wrinkled interfaces in soft multi-layered composites through experiments, analytical models and numerical simulations. Instabilities have been a subject of study in a number of composite material systems where structural mechanics approaches, energy methods, and Bloch wave analyses, have been found to predict this complex phenomenon. The main objective of this paper is to explore and predict instabilities in the interfacial layers of layered composites (details are provided in Supporting Information S1–S3). Prototypes of soft multi-layered polymer composites are