Thermal Resilience and Multidirectional Dielectric Anisotropy Decay in Oriented β-PVDF Films: 3D Permittivity–Viscoelastic Correlations Across the α-Relaxation Transition

Abstract

[Abstract] This study quantifies the three-dimensional dielectric anisotropy of oriented β-PVDF films and its thermal evolution using multi-axis impedance spectroscopy. Results reveal a 35% in-plane permittivity contrast (ε2 > ε1) and an 11% out-of-plane enhancement (ε3 > ε2), demonstrating that dipole alignment exceeds mechanical orientation. Two thermal regimes are identified: a stable state below approximately 65 °C and an orientation-collapse region initiating at this temperature, concurrent with the crystalline α-relaxation onset. Dielectric anisotropy declines from 38% to below 15% above 70 °C, a loss that parallels the mechanical modulus decay, thereby confirming coupled dielectric–viscoelastic relaxation. Differential scanning calorimetry (DSC) validates the thermal transitions governing collapse. These findings establish structure–property stability limits for β-PVDF, enabling reliable performance prediction in piezoelectric sensors, anisotropic capacitors, and multilayer films. The method also provides a non-destructive framework for three-dimensional dielectric quality control in polymer manufacturing.