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

柔性电子产品在健康和环境监测方面具有诱人的潜力。这些设备的一个关键组成部分是由嵌入柔性弹性体中的金属薄片组成的导电油墨提供的电连接。这种复合连接器必须即使在重复加载（例如拉伸）之后也保持导电。目前，对循环负载如何影响电流的电阻的知识有限。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至关重要。该奖项旨在通过实验和模型建立对导电复合油墨在循环负载下的机械和电气响应的理解。这项工作可以指导可拉伸电子产品的设计，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。该奖项还支持在校园和远程学习的学生在本科和研究生课程的新类为基础的项目的发展。此外，可穿戴电子学习模块将在当地县的中学生与大量的代表性不足的少数民族population.The这项工作的目的是获得一个基本的理解的机械和电气性能之间的关系的金属聚合物复合油墨的可穿戴和可拉伸应用时，受到单调和循环加载，特别是应变局部化的重点。直观地假设，局部变形决定了导电逾渗网络的演变并影响所得电阻。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将用于了解应变局部化的机制起源，并量化其在各种加载条件下的演变。这些实验还将产生关于金属薄片和空隙的统计分布的数据集，这些数据集将用于了解金属化网络的演变。几个灵活的和可拉伸的油墨将根据材料性能，缺陷分布，和薄片体积分数进行研究。最后，现有的渗流模型将加强与时空描述这些分布，以产生互补的数据，预测电阻演变，并提供复合油墨的设计guidelines.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.