Beyond wrinkles and creases: Generalized and tailored instabilities of polymer films

最近关于聚合物表面机械不稳定性的实验和理论进展提供了对两种基本不稳定性模式的很好的理解：由软基板上的硬膜屈曲驱动的起皱，以及由软基板本身屈曲驱动的折痕。然而，在生物和技术背景下发现的真实材料系统往往表现出多样性的行为，这些行为无法仅基于这些简单的范式来解释，因为与迄今为止仔细研究的简单模型系统相比，在几何和材料特性方面具有更大的复杂性。该项目旨在通过对弹性双层中发生的表面屈曲模式的全面描述，以及两层之间厚度和刚度的不匹配，以及每层所感受到的压缩水平，来促进对聚合物表面不稳定性的理解。实验将定量表征不同不稳定模式的发生和发展，这些不同状态之间的过渡机制，以及加载和卸载循环时迟滞和双稳性的存在。与有限元模型的比较将进一步深入了解这些行为的驱动力。屈曲力学是广泛现象的核心，从生物学中功能结构的发展到消费电子中微机电设备的操作。该项目旨在提供对两种基本表面屈曲模式之间相互作用的综合理解，这对聚合物材料至关重要。它将提供模型实验系统，为提高我们对生物学和疾病（如哮喘）中形态发生过程的理解提供潜力，并将为具有可切换特性（如粘附性和光学透明度）的技术适用材料开辟新的途径。该项目还将为不同群体的参与者提供指导和研究机会，包括高中学生和教师、研究生和本科生。将与附近学区的教师和学生建立持久的伙伴关系，这些学区为大量代表性不足的少数民族学生提供服务，以帮助实现该领域的多样化。

TECHNICAL SUMMARY Recent experimental and theoretical progress on mechanical instabilities of polymer surfaces has provided a good understanding of two fundamental modes of instability: wrinkling, driven by buckling of a stiff film on a soft substrate, and creasing, driven by buckling of the soft substrate itself. However, real material systems found in biological and technological contexts often show a diversity of behaviors that defy explanation based on these simple paradigms alone, due to the greater complexity in terms of both geometry and material properties when compared to the simple model systems that have been carefully studied to date. This project seeks to advance understanding of polymer surface instabilities by developing a comprehensive picture of the landscape of surface buckling modes that occur in elastic bilayers, as parameterized by the mismatch in thickness and stiffness between the two layers, as well as the level of compression felt by each. Experiments will be carried out to quantitatively characterize the onset and development of different instability modes, the mechanisms of transitions between these different states, and the presence of hysteresis and bistability upon cycles of loading and unloading. Comparisons with finite element models will provide further insights into the driving forces for each of these behaviors.NON-TECHNICAL SUMMARYBuckling mechanics are central to a wide range of phenomena, ranging from the development of functional structures in biology, to the operation of micro-electromechanical devices in consumer electronics. This project seeks to provide an integrated understanding of the interplay between two fundamental surface buckling modes that are of key importance for polymeric materials. It will provide model experimental systems that offer the potential to improve our understanding of morphogenetic processes in biology and diseases such as asthma, and will also open new routes to technologically applicable materials with switchable properties such as adhesion and optical transparency. The project will also provide mentoring and research opportunities for a diverse group of participants including high school students and teachers, graduate students, and undergraduates. Lasting partnerships with teachers and students from nearby school districts that serve large populations of under-represented minority students will be developed to aid in efforts to diversify the field.