Tuning the Screening Effect on Optical Properties of Flexible PVA Films via the Synergistic Incorporation of Nano-La2CuO4, Electrolytic LiClO4, and Varied Plasticizer PC Content

The development of flexible, leakage-free solid polymer electrolytes (SPEs) represents a critical milestone for the societal transition toward sustainable, high-safety portable electronics and smart optical displays. This work addresses this need through the novel fabrication of flexible nanocomposite membranes via a streamlined solution-casting approach, uniquely achieving precision tuning of the electronic screening effect within a host poly(vinyl alcohol) (PVA) matrix. The PVA matrix incorporates 2 wt % La2CuO4 nanoparticles (verified at 80–120 nm via TEM), 10 wt % LiClO4 electrolytic salt, and varying fractions (2 to 8 wt %) of propylene carbonate (PC) plasticizer. FTIR spectroscopy confirmed robust complexation, showing systematic red shifts (downshifts) in the host matrix O–H (∼21 cm–1) and C═O (∼10 cm–1) stretching bands, driven by extensive ion-dipole coordination networks. SEM and XRD analyses indicated a highly amorphous microstructure within the plasticized matrices. DSC thermograms verified superior film flexibility, with the glass transition temperature (Tg) systematically dropping from ∼98 °C to ∼66 °C. Optical metrics revealed that the direct optical bandgap (Eg) was nonlinearly tuned, initially decreasing from 5.22 eV (pure PVA) to 3.29 eV at 2 wt % PC, and subsequently expanding to 3.79 eV up to 8 wt % PC due to a prominent screening/capping effect. Concurrently, the refractive index at 250 nm systematically shifted from 1.78 to 3.00, while the optimal 2 wt % PC loading yielded a peak optical conductivity of 8.11 × 1011 s–1. These data-driven findings confirm that this tunable composite matrix bridges the gap between film flexibility and precise optoelectronic modulation.