Advancing green electronics: tunable piezoelectric enhancement in biodegradable poly(L-lactic acid) PLLA films...

The rising interest in biodegradable polymers like PLLA is gaining attention for their potential in next-generation biomedical devices. One of the critical challenges in leveraging PLLA's full potential is enhancing its crystallinity, as it greatly influences mechanical, thermal, degradation, and piezoelectric properties, which are essential for various applications. Here, we use thermal annealing and strain engineering to transform the amorphous phase into a more ordered crystalline structure. Through various characterization techniques, we show that crystallinity increased progressively from 34.8% in unprocessed films to 57.4% at 100% strain. Terahertz time-domain spectroscopy is employed to gain insights into the structural and dynamic properties where we study low-frequency molecular vibrations and anisotropic properties, enabling simultaneous evaluation of structural, such as crystallinity, and optical characteristics. Rotational analysis provides direct evidence of molecular orientation and birefringence induced by mechanical processing. These findings align strongly with the traditional characterization techniques (XRD, WAXS, DSC, and FTIR). Piezoresponse force microscopy shows that the VPFM signal increased from 0.65 ± 0.15 pm V^-1 in unprocessed films to 6.5 ± 1.5 pm V^-1 at 100% strain. The in-depth work is an important step in gaining a deeper understanding of how the crystalline regions form, evolve under different processing conditions, and influence PLLA's overall properties.