Origins of Electromechanical Behavior in Surface-Localized Nanocomposites: Insights into Crack Network Dynamics and Particle Network Rearrangements

There is a critical need for new technologies to support lunar and Martian exploration efforts, particularly for flexible, durable, and environmentally stable materials that can weather challenging space conditions. Electrically conductive thin films are critical for numerous applications, including structural health monitoring, charge dissipation, micrometeoroid and orbital debris impact detection, and electrodynamic dust shielding. Surface-localized nanocomposites (SLNCs) offer a promising alternative to metallic and ceramic films as flexible, durable, thin film conductors. This study examines the electromechanical properties in tension and bending of SLNCs produced via melt infiltration with chemically modified reduced graphene oxide (CMrGO) as the conductive component with three polymer materials which serve as both the substrate and the composite matrix in the SLNC: olefin block copolymer (OBC), high-density polyethylene (HDPE), and poly-(vinylidene fluoride) (PVDF). Monotonic electromechanical tensile testing revealed a substrate independent, linear piezoresistive response in the elastic regime and highly substrate dependent nonlinear piezoresistive response beyond yield. Substrate ductility strongly affected the measurable gauge factor (GF) in these systems, with OBC and HDPE SLNCs having GFs of 20-100, compared to only 2 for PVDF. Static bending tests showed small changes in resistance even at sharp bending radii. The low GF in the elastic regime and at sharp bending radii is beneficial for both active and passive electronic applications for inflatable structures, drapeable covers, and flexible robotics. In situ microscopy during uniaxial tensile deformation identified crack network development as a key mechanism contributing to the nonlinear piezoresistive response after yield. Optical profilometry revealed the formation of partial thickness cracks at low strains which grew deeper and wider with increasing strain. Finally, cyclic testing indicated that in addition to crack formation and closure, particle network rearrangement associated with matrix relaxation plays a significant role in the piezoresistive response, particularly in the elastic regime.