Infrared photothermal enhancement of piezoelectricity in γ-glycine/PVA films via targeted interfacial hydrogen bond engineering

Abstract

Flexible γ-glycine–polyvinyl alcohol (PVA) piezoelectric thin films demonstrate potential applications for implantable/wearable biomedical devices, but suffer from low piezoelectricity due to random dipole self-alignment of the γ-glycine molecule. Herein, we propose an infrared (IR) illumination strengthening the interfacial hydrogen bond strategy to enhance the piezoelectricity of γ-glycine film. Considering the critical role of hydrogen bonding between γ-glycine's carboxylate (COO⁻) and PVA's hydroxyl (–OH) groups in dipole polarization, films were selectively illuminated using pulsed IR lasers with the wavenumber of 1588 cm⁻¹ (COO⁻ group) and 3436 cm⁻¹ (–OH group), respectively. This IR irradiation induces strong, localized photothermal expansion within these functional groups, intensely stretching interfacial hydrogen bonds and consequently promoting dipole alignment parallel to the film thickness direction. This approach yields remarkable piezoelectric improvements in low-piezoelectricity regions increasing from 3.5 to 8.5 pC N⁻¹ (at 1588 cm⁻¹) and 3.5 to 8.1 pC N⁻¹ (at 3436 cm⁻¹), while high-piezoelectricity regions exhibit the maximum piezoelectricity up to 9.8 pC N⁻¹. IR-enhanced piezoelectric values approach the theoretical maximum (10.4 pC N⁻¹) of γ-glycine film. This work provides a promising hydrogen-bond engineering route to enhance the piezoelectricity of bio-piezoelectric materials for next-generation medical devices.