Enhanced Piezoelectric Strain Sensitivity in Electrospun PVDF/MWCNT Nanofibers via Moderate Mechanical Stretching and β-Phase Orientation

Electrospun poly(vinylidene fluoride) (PVDF)–based nanofibrous composites have attracted considerable interest for flexible and wearable strain-sensing applications due to their intrinsic piezoelectricity, low density, and mechanical compliance. In this study, PVDF/multi-walled carbon nanotube (MWCNT) nanofibrous composites were fabricated via electrospinning to systematically investigate the combined effects of CNT loading and in-process mechanical stretching on morphology, crystalline structure evolution, mechanical properties, and piezoelectric strain sensitivity. MWCNT contents of 0.05, 0.2, and 0.5wt% were incorporated into PVDF solutions electrospun under fixed parameters, with nanofibers collected under random and mechanically stretched (using a rotating drum collector at 500 rpm) conditions. Structural and phase analyses (SEM, XRD, FT-IR) revealed that the synergistic action of jet stretching and CNT-induced nucleation significantly enhanced the content and dipole orientation of the electroactive β-phase, particularly at 0.05wt% CNT loading. Mechanical testing demonstrated that stretched nanofiber mats exhibited superior tensile strength and stability compared to random mats. Piezoelectric measurements under dynamic loading showed that the stretched PVDF/MWCNT nanofibers containing 0.05wt% CNT generated the highest output voltage (~ 4.9 mV) and strain sensitivity (1.84 mV·N⁻¹). These results demonstrate a clear processing–structure–property relationship and identify optimal electrospinning conditions for high-performance, flexible PVDF-based strain sensors.