Biobased Wrinkled Surfaces Induced by Wood Mimetic Skins upon Drying: Effect of Mechanical Properties on Wrinkle Morphology.

We previously developed biobased wrinkled surfaces based on wood mimetic skins in which microscopic wrinkles were fabricated on a chitosan film by immersion in a phenolic acid solution, horseradish peroxidase-catalyzed surface reaction, and drying. Here, we prepared a diverse range of wrinkled films by immersion treatment at 30, 40, 50, and 60 °C in p-coumaric acid and then investigated the correlation between wrinkle morphology and mechanical properties. Wrinkle wavelengths gradually decreased as the immersion temperature increased as well as the previous report. In order to clarify the mechanisms responsible for the different wrinkle morphologies, the films were subjected to elastic moduli measurement and GPC analysis after immersion treatment. These experiments provided evidence that the chitosan around the film surface decomposed along with the immersion process. The decomposition was accelerated by higher immersion temperature, suggesting that higher temperatures led to the formation of softer skins, inducing smaller wrinkles. In fact, wrinkle morphologies with this system were predominately determined by the hardness of the wood mimetic skins. This phenomenon is consistent with the fundamentals of surface wrinkling in nature. This study is the first to demonstrate that artificial wrinkling triggered by water evaporation can be controlled by precise control of the surface hardness of soft material.