Composition-Tunable Core−Shell Architecture in Electrospun Nanofibers Enables Task-Specific Electret and Piezoelectric Devices

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Poly(vinylidene fluoride) (PVDF) combines flexibility, a high dielectric constant, and considerable piezoelectric responsiveness, making it promising for sensing and self-powered systems. Herein, composite nanofibers with a multiphase spatial architecture were fabricated via one-step electrospinning of PVDF and polyurethane (PU) blends. Adjusting the blending ratios induced spontaneous phase separation and thereby tuned the composition of the outer region, resulting in a composition-tunable core−shell architecture. Selective PU removal and XPS surface analysis were used to characterize the composition-dependent outer-region structure. We demonstrate that this structural variation enables the rational design of task-specific applications. At a balanced blending ratio, both components were detected within the surface region. The balanced composition reduced charge loss under high-humidity conditions and enabled sustained water-droplet energy harvesting. Conversely, a PVDF-rich composition formed a PVDF-shell architecture that was directly subjected to external mechanical stress. This configuration enabled efficient stress transfer, generating a maximum power density of 3.04 mW/m2 and demonstrating its potential for piezoelectric motion sensing. Ultimately, this strategy provides a composition-tunable approach to addressing the persistent design challenge of balancing environmental stability and piezoelectric output within a single-material system, offering an adaptable framework for task-specific flexible electronics.