Eu-modified poly (L-lactic acid) microspheres with enhanced crystallinity and stability by incorporation of rare-earth ions interacting with polymer chains via temperature-tuned emulsification

Abstract

Incorporation of lanthanide ions into polymers via rare-earth organic complexes poses the issue of the interaction between the polymer matrix and lanthanide compounds, which can significantly influence both the rare-earth functional properties and the structural features of the matrix. This work investigates the synthesis of europium-containing poly (L-lactic acid) (PLLA) microspheres through an oil-in-water emulsion of PLLA and europium (III) acetylacetonate hydrate dissolved in dichloromethane and water containing poly (vinyl alcohol). The synthesis was conducted at various temperature – from 20 °C to 80 °C, including conditions above the PLLA glass transition. Results from X-ray diffraction and Raman scattering give evidence of higher crystallinity in Eu-modified PLLA microspheres than in undoped PLLA, while differential scanning calorimetry indicates that Eu addition hinders PLLA chain mobility with a resulting decrease in PLLA melt crystallization ability. Insights into the incorporation mechanisms of Eu³⁺ in the microspheres were provided by photoluminescence, scanning-electron-microscopy, micro-computed-tomography, X-ray fluorescence, and infrared spectroscopy. The analysis shows that Eu³⁺ complexes enter the polymer structure by interacting with PLLA chains, modifying the local environment of the lanthanide ions. These findings finally provide a new basis for designing tailored synthesis methods for specific applications.