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

该奖项支持在各种聚合物材料上开发可控表面皱纹和褶皱的基础研究。材料的表面属性在许多应用中都很重要。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，这些特性在其他方面是不可用的，例如具有可调附着力和自清洁特性的智能表面。一种可行的控制表面纹理的方法是产生表面皱纹，这可以通过机械压缩附着在相对柔顺的基材上的薄膜涂层来轻松实现。对于薄膜和衬底材料都是弹性的情况，目前对这一领域的理解是成熟的。然而，许多实际应用涉及的聚合物材料不是弹性的，而是粘性或粘弹性的，具有随时间变化的机械性能。此外，通过增加压缩，可以在聚合物表面获得具有局部折叠的复杂表面纹理。这项研究将使使用皱纹表面来控制润湿性、摩擦和粘合以及刺激响应型智能表面在能源、医疗保健、航空航天和汽车行业的潜在应用成为可能。因此，这项研究的结果将有利于美国的经济和社会。这项研究涉及两个机构和跨学科的合作，包括力学、材料科学和化学工程。这种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。过去对起皱的研究主要集中在附着在柔软弹性衬底上的薄膜上。然而，在粘弹性基材上，起皱是受动力学限制的，并且起皱图案本质上取决于压缩速度。这项研究的主要假设是，通过使用精心选择的模型聚合物材料，可以利用弹性极限和粘性极限之间的起皱行为的整个光谱。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对聚合物支撑的薄膜施加良好控制的大压缩变形，该方法允许单独考察应变和应变率的影响。基于有限元方法的数值模拟将与实验相结合，以了解其潜在机制并预测褶皱和折叠结构的形成。除了直接关注粘弹性衬底，这个项目还将广泛地阐明耗散效应在自然界中观察到的一系列褶皱和折叠现象中的作用。

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.