Morphology and Glass Transition of Thin Polylactic Acid Films

The aim of this study is to highlight the effect of the morphology of polylactic acid (PLA)thin films on the glass transition in this confined geometry. For that purpose, poly(L-lactic acid)and poly(D-lactic acid)polymer films were prepared on different surfaces such as mica and silicon surfaces by using two different solvents. The films exhibit different morphologies starting from individual macromolecular chains at very low concentration to homogeneous films at higher concentrations. Globular to elongated rodlike structures of the PLA macromolecules were observed according to the polarity of the surface and the solvent. The Tg of PLA enantiomeric film, determined by adhesion force using atomic force microscopy (AFM)as a function of temperature, was confirmed by ellipsometric measurements. Surprisingly, this value is independent of the morphology of thin enantiomeric film. A balance between the attractive surface effects and a decrease of the crystallinity of PLA on the mobility in the amorphous region will be discussed