SUMMARY

Flexible hybrid electronics (FHE) devices have gained increasing research interest due to their potential for widespread applications in healthcare and environmental monitoring. These devices combine electronic components with compliant electrical circuitry based on stretchable and flexible conductive interconnects. One class of conductive interconnects is the composite conductive ink consisting of conductive metal flakes embedded in a polymer binder and deposited on a polymer substrate. The primary objective of the proposed research is to advance the fundamental understanding of the relationship between the mechanical and electrical behaviors of selected conductive inks subjected to monotonic and cyclic stretching. Specifically, the research focuses on investigating the origins of ink strain localizations and identifying their relationship to the electrical resistance increase that occur during monotonic uniaxial tensile straining or cyclic uniaxial straining between two strain values. Localized ink deformation is examined in detail through in-situ electron scanning microscopy (SEM) and confocal microscopy experiments with synchronous electrical resistance measurement and aided by focused ion beam (FIB) cross-sectioning. The information on the ink microstructure evolution and overall damage pattern gained from the in-situ experiments will contribute to the modeling of ink strain localization and electrical behavior. In addition, the proposed research also explores ways to predict an ink’s electrical performance with cyclic strain based on the resistance evolution data collected from the monotonic and cyclic experiments. Key empirical parameters related to the resistance evolution are identified and used to construct predictive models and experimental protocols for characterizing the ink’s electrical performance with cyclic strain.