Strain Localization in Composite Inks and its Effect on Electrical Behavior under Monotonic and Cyclic Stretching

灵活的电子产品在健康和环境监测方面提供了诱人的潜力。这些设备的一个关键组件是由导电油墨提供的电气连接，这些油墨由嵌入柔性弹性体中的金属薄片组成。即使在重复加载(如拉伸)之后，这种复合连接器也必须保持导电性。目前，对循环载荷对水流阻力的影响知之甚少。对导体灾难性故障的原因也知之甚少，这对于电流可能中断的生命关键应用是必不可少的。该奖项旨在通过实验和模型建立对导电复合油墨在循环载荷下的机械和电学响应的理解。这项工作可以指导可伸缩电子设备的设计，并确保此类设备在包括健康监测在内的一系列应用中的可靠性。该奖项还支持为在校和远程学习的学生开发本科和研究生课程的新班级项目。此外，还将为少数民族人口较少的当地县的中学生开发可穿戴电子学习模块。这项工作的目标是从根本上了解可穿戴和可拉伸应用的金属-聚合物复合油墨在单调和循环载荷下的机械和电气行为之间的关系，重点是应变局部化。可以直观地认为，局域变形决定了导电渗流网络的演化，并影响了所产生的电阻。将使用原位扫描电子显微镜和光学共聚焦显微镜以及聚焦离子束切片来了解应变局部化的机制起源并量化其在不同加载条件下的演化。这些实验还将产生关于金属薄片和空洞的统计分布的数据集，这将被用来理解渗流网络的演变。将根据材料特性、缺陷分布和薄片体积分数来研究几种柔性和可拉伸油墨。最后，现有的渗流模型将通过对这些分布的时空描述来增强，以产生补充数据，预测电阻演变，并提供复合墨水设计指南。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Flexible electronics offer tantalizing potential in health and environmental monitoring. A crucial component of these devices is the electrical connection provided by conductive inks consisting of metallic flakes embedded in a flexible elastomer. Such composite connectors must remain conductive even after repetitive loading, such as stretching. Presently, there is limited knowledge of how the resistance to current flow is affected by cyclic loading. There is also little understanding of the causes of catastrophic failure of the conductor, which is essential for life-critical applications where current flow may be interrupted. This award seeks to establish an understanding of the mechanical and electrical response under cyclic loading for conductive composite inks through experiments and models. This effort can guide design of stretchable electronics and ensure reliability of such devices in a range of applications including health monitoring. The award also supports development of new class-based projects in undergraduate and graduate courses for both on campus and remote learning students. Additionally, wearable electronics learning modules will be developed for middle schoolers in the local counties with large underrepresented minority populations.The objective of this work is to obtain a fundamental understanding of the relationship between mechanical and electrical behavior of metal-polymer composite inks for wearable and stretchable applications when subjected to monotonic and cyclic loading, with a specific focus on strain localization. It is intuitive to assume that localized deformation dictates the evolution of the conductive percolation network and affects the resulting resistance. In-situ scanning electron microscopy and optical confocal microscopy, as well as focused ion beam sectioning will be used to understand the mechanistic origins of strain localization and quantify its evolution under various loading conditions. These experiments will also produce datasets on the statistical distribution of metallic flakes and voids, which will be used to understand the evolution of the percolating network. Several flexible and stretchable inks will be investigated based on material properties, defect distribution, and flake volume fraction. Lastly, an existing percolation model will be enhanced with spatiotemporal descriptions of these distributions to produce complementary data, predict electrical resistance evolution, and provide composite ink design guidelines.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.