RUI: The Origins of Statistical Variation of Strength in Micropatterned Adhesive Contacts

该基金研究了现实世界表面的粗糙度特性与新型可控和可重复使用的粘合表面的性能之间的关系。基于微型结构阵列的表面图案，从昆虫和蜥蜴的脚掌中获得灵感，这些粘合剂可以在多次重复循环中在强烈附着和容易分离之间转换。这可能会使在极端环境中（如真空和水下）抓握精致物体或创建多功能界面（如生物医学诊断和治疗）的新能力成为可能。每个微图型亚接触处界面缺陷的差异导致局部粘接性能的变化，其统计特性影响粘接片的整体强度和稳定性。这项工作将建立关系，使预测新出现的统计行为和由此产生的粘合剂性能，基于接触面的特性。这笔拨款还将加强加州州立大学北岭分校机械工程专业学生的研究型教育活动，其中65.6%的学生来自传统上得不到充分服务的少数民族。该范围将通过基于课程的本科项目扩展，允许大量学生为实现研究目标贡献有意义的数据。此外，参与的学生将担任本科生导师，并围绕该主题举办高中外展研讨会。本研究将解决理解上的几个关键空白。亚触点的粘接强度仅对理想缺陷进行表征，并且将考虑缺陷尺寸，形状和位置的综合范围。微观结构剥离的内聚区有限元模拟将提供缺陷性能变化时的强度。粗糙表面上的缺陷形成尚不清楚，必须进行检查，以将表面特征与粘合强度的统计分布联系起来。分子动力学模拟将产生接触图，因为物体的粗糙度和弹性特性的光谱性质是不同的。微图型粘合剂的实验表征将在具有制造缺陷和随机粗糙度的表面上进行，以验证通过建模和仿真获得的关系。最后，必须扩大对亚接触粘接强度的统计变化对近似临时粘接应用的长度和时间尺度性能的影响的理解。粘接贴片行为的半解析力学模型将整合这种局部变化，并检查基材曲率、加载率和贴片尺寸对整体粘接性能的综合影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This grant investigates the relationship between the properties of roughness on real-world surfaces and the resulting performance of novel controllable and reusable adhesive surfaces. Based upon patterning surfaces with arrays of microscale structures, taking inspiration from the toepads of insects and lizards, these adhesives can transition between strong attachment and easy detachment over many repeat cycles. This may enable new capabilities in gripping of delicate objects in extreme environments (e.g. in vacuum and underwater) or in the creation of multifunctional interfaces (e.g. in biomedical diagnostics and therapeutics). Differences in interfacial defects at each micropatterned sub-contact results in variation in local adhesive performance, with the statistical properties influencing the global strength and stability of the adhesive patch. This work will establish relationships which enable prediction of the emerging statistical behavior and resulting adhesive performance, based upon characteristic properties of the contacting surfaces. This grant will also strengthen research-based educational activities for the Mechanical Engineering student body at California State University Northridge, of whom 65.6 percent are from traditionally underserved minorities. The reach will be extended through a course-based undergraduate project, allowing a large volume of students to contribute meaningful data toward achieving the research objectives. Additionally, participating students will serve as undergraduate mentors and run high school outreach workshops themed around the topic.Several key gaps in understanding will be addressed in this study. The adhesive strength of sub-contacts has only been characterized for idealized defects, and a comprehensive range of defect size, shape, and position will be considered. Cohesive zone finite element simulations of microstructural detachment will provide the strength as defect properties are varied. Defect formation on rough surfaces is not understood, and must be examined to relate the surface characteristics to the statistical distribution of adhesive strength. Molecular dynamics simulations will yield contact maps as spectral properties of the roughness and the elastic properties of the bodies are varied. Experimental characterization of micropatterned adhesives will be performed on surfaces with manufactured defects and random roughness to validate relationships obtained through modeling and simulation. Lastly, understanding of the influence of statistical variation in sub-contact adhesive strength on performance at length and time scales approximating temporary bonding applications must be expanded. A semi-analytical mechanical model of adhesive patch behavior will integrate this local variation and examine the combined effects of substrate curvature, loading rate, and patch size on the global adhesive performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.