Molecularly induced β-phase enhancement and piezoelectric response in all-organic PVDF-F16CuPc composite films

Abstract

Poly(vinylidene fluoride) (PVDF) is a fluoropolymer that is particularly promising for its electroactive, beta-phase-dependent functional performance. This study elucidates an all-organic composite approach to effectively alter the fraction of polar beta-phase formation in PVDF through the incorporation of an organic small molecule filler, fluorinated copper phthalocyanine (F16CuPc). Our studies using Fourier-transform infrared spectroscopy reveal an 88% enhancement of the polar beta-phase fraction, particularly at an optimal filler concentration of 2 wt% F16CuPc, relative to pristine PVDF. Studies using X-ray diffraction measurements corroborate this phase transformation by showing a preferential stabilization of the beta-phase and suppression of the nonpolar alpha-phase. Piezoresponse force microscopy further confirms the enhancement in nanoscale piezoelectric behavior, demonstrating a 20% increase in the piezoelectric coefficient (d33) upon optimal F16CuPc loading compared to pristine PVDF. This enhancement in beta-phase fraction upon optimal F16CuPc incorporation is mainly driven by highly electronegative fluorine-mediated C-F & centerdot;& centerdot;& centerdot;H-C interactions with the -CH2- dipole, along with electrostatic coupling between the Cu center and the -CF2- dipole. This cross-interaction between the fluorinated filler and fluoropolymer chains promotes conformational reorganization from the trans-gauche to the all-trans configuration, thereby stabilizing beta-phase formation. Our studies reveal that fluorinated metal phthalocyanines act as efficient electroactive beta-phase inducers in fluoropolymers without limiting mechanical compliance or electromechanical integration, thereby extending their applications in next-generation flexible energy harvesters, sensors, and wearable smart electromechanical devices.