Collaborative Research: Wrinkling and Folding of Thin Films on Viscoelastic Substrates by Experiments and Modeling

该奖项支持基础研究，以开发各种聚合物材料的可控表面褶皱和折叠。材料的表面性质对于许多应用是重要的。设计和控制表面纹理的能力将为实现材料表面特性提供机会，这些特性是不可用的，例如具有可调粘附力和自清洁特性的智能表面。可控表面纹理的一种可行方法是产生表面褶皱，这可以通过机械压缩附着到相对柔顺的基底材料的薄膜涂层来容易地实现。目前在这一领域的理解是发达的情况下，薄膜和基板材料都是弹性的。然而，许多实际应用涉及聚合物材料，其不是弹性的，而是粘性的或粘弹性的，具有时间依赖性的机械性能。此外，通过增加压缩，可以在聚合物表面上实现具有局部折叠的复杂表面纹理。这项研究将使潜在的应用程序，使用纹理表面控制润湿性，摩擦和粘附，以及刺激响应智能表面在能源，医疗保健，航空航天和汽车行业。因此，这项研究的成果将有利于美国的经济和社会。这项研究涉及两个机构之间的合作和跨学科，包括力学，材料科学和化学工程。跨学科的合作将有助于扩大来自不同背景的研究参与，并对工程教育产生积极影响。过去对薄膜的研究主要集中在附着在软弹性基底上的薄膜上。然而，在粘弹性基材上，起皱是动力学限制的，并且起皱图案本质上取决于压缩速率。本研究的主要假设是，整个频谱的弹性和粘性极限之间的摩擦行为可以利用精心挑选的模型聚合物材料。研究小组将进行计算和实验研究。将开发一种简单而优雅的方法来施加良好控制的大压缩变形的聚合物支撑的薄膜，这使得应变和应变率的影响进行独立检查。基于有限元法的数值模拟将与实验结合进行，以了解潜在的机制，并预测皱纹和折叠结构的形成。除了直接关注粘弹性基板，这个项目将广泛阐明耗散效应在自然界中观察到的广泛的扭曲和折叠现象的作用。

This award supports fundamental research to develop controllable surface wrinkles and folds on a variety of polymeric materials. Surface properties of a material are important for many applications. The capability to design and control surface texture would open opportunities to realize material surface properties that are otherwise unavailable, such as smart surfaces with tunable adhesion and self-cleaning properties. One viable approach to controllable surface texture is to create surface wrinkles, which can be accomplished easily by mechanically compressing a thin film coating attached to a relatively compliant substrate material. Current understanding in this field is well-developed for situations when both the thin film and the substrate material are elastic. However, many practical applications involve polymeric materials that are not elastic, but either viscous or viscoelastic, with time-dependent mechanical properties. Furthermore, complex surface textures with localized folds may be achieved on polymer surfaces by increasing compression. This research will enable potential applications using wrinkle-textured surfaces for controlling wettability, friction and adhesion, as well as stimulus responsive smart surfaces in energy, healthcare, aerospace, and automotive industries. Therefore, results from this research will benefit the U.S. economy and society. This research involves a collaboration between two institutions and across disciplines including mechanics, material science, and chemical engineering. The interdisciplinary collaboration will help broaden participation in research from diverse background and positively impact engineering education.Past research on wrinkling has focused predominantly on thin films attached to soft elastic substrates. On viscoelastic substrates, however, wrinkling is kinetically-limited, and the wrinkle patterns intrinsically depend on the rate of compression. The primary hypothesis of this research is that the entire spectrum of the wrinkling behavior between the elastic and viscous limits can be exploited by using well-selected model polymeric materials. The research team will perform both computational and experimental studies. A simple and elegant method will be developed to impose well-controlled large compressive deformation on polymer-supported thin films, which allows the effects of strain and strain rate to be examined independently. Numerical simulations based on finite element method will be conducted in conjunction with experiments to understand the underlying mechanisms and to predict formation of wrinkles and folding structures. Beyond the immediate focus on viscoelastic substrates, this project will broadly elucidate the role of dissipative effects in a wide range of wrinkling and folding phenomena observed in nature.