Absorption of water molecules on the surface of stereocomplex-crystal spherulites of polylactides: An in-situ FT-IR spectroscopy investigation

The correlation between water molecules and polylactide was clarified. The crystallinity in stereocomplex (SC) crystal spherulites was investigated using microbeam wide-angle X-ray diffraction. The crystallinity was higher in the central region, and edge-on lamellae grew in a twisted manner. The hydrogen bonding in SC-crystal spherulites was evaluated via microbeam FT-IR spectroscopy in a humidity-controlled cell. The water-derived bands corresponding to OH vibration and HOH bending increased with increasing humidity. Microbeam FT-IR spectroscopy was used to evaluate the water absorption behavior of crystalline films depending on their position. Coarse-grained molecular dynamics simulations indicated that the number of adsorbed water molecules increased with decreasing crystallinity. In SC-crystal spherulites, water molecules are absorbed in both amorphous and crystalline regions but with greater difficulty in the crystalline regions. These insights into water molecule absorption on SC-crystal spherulite can facilitate the development of polylactide materials with controlled biodegradability for advanced medical and optical applications.