Frictional Unlocking and Energy-Controlled Constrained Densification in Nanoparticle Networks

Nanoparticle networks, characterized by strong interparticle adhesion and structural rigidity, are typically considered resistant to dynamic reorganization under mechanical perturbation, unlike thixotropic gels or granular materials that fluidize when agitation exceeds critical thresholds. Using high-resolution atomic force microscopy (AFM) coupled with dynamic mechanical analysis, this study examines a frictional unlocking mechanism in porous sintered silver nanoparticle networks, where small oscillatory strains trigger a reversible transition from a purely elastic to elastoplastic response. This nanoscale reorganization occurs through intermittent particle rearrangements that enable localized mobility while maintaining global network integrity, mediated by the conversion of oscillatory energy into grain-boundary shear. The results indicate that this mechanism represents one stage of a broader constrained densification pathway, in which nanoparticle networks evolve from a fluid-like, loosely connected state through distinct intermediate metastable configurations, each separated by well-defined energy barriers, before reaching a reversible solid-like state. This stepwise progression, quantified through energy dissipation measurements and microstructural analysis, contrasts with classical unjamming or liquefaction phenomena by preserving the structural continuity throughout the transition. By establishing links between nanoscale energy dissipation pathways and macroscopic mechanical responses, this work provides a framework for designing materials with tunable stiffness and dynamic adaptability. The findings are relevant to technologies such as electronic interconnects with stress-adaptive properties, powder-based additive manufacturing processes, and energy storage systems, where controlled nanoparticle mobility under operational stresses is important for long-term performance.