Morphological diagram for metal/polymer bilayer wrinkling: Influence of thermomechanical properties of polymer layer

Three types of wrinkling are found to occur in the wrinkling of a bilayer of metal and polymer on a substrate. Each type has its own unique characteristics in terms of the wrinkle growth and strain behavior. While the characteristics can be grouped into three types, five distinct wrinkling regimes exist in terms of morphological change: evolutionary, constrained evolutionary, instantaneous, unconstrained, and spinodal wrinkling. The final morphologies for these wrinkling regimes are as follows: a labyrinth structure for the evolutionary wrinkling, an island structure for the constrained evolutionary and instantaneous wrinkling, a flat surface for the unconstrained wrinkling, and a mountainous structure for the spinodal wrinkling. A morphological diagram for these regimes and types can be constructed in terms of temperature and thickness of the polymer film with the molecular weight as a parameter. The characteristics and morphology are governed by the thermomechanical properties of the polymer as affected by temperature with the constraints stemming from strain saturation of the metal and pinning of the thin bilayer.