Atomic Force Microscopy Observation of Polylactide Stereocomplex Edge-On Crystals in Thin Films: Effects of Molecular Weight on Lamellar Curvature.

The shapes of the edge-on lamellar crystals of equiweight poly(l-lactide) (PLLA)/poly(d-lactide) (PDLA) stereocomplexes with various combinations of molecular weights were investigated by using atomic force microscopy. In the cases of the PLLA/PDLA blends with equivalent molecular weights, the straight-shaped edge-on lamellae were observed. On the other hand, the curved edge-on crystals were able to be seen for the PLLA/PDLA stereocomplexes with nonequivalent molecular weights. It was revealed that the direction of lamellar curvature in the polylactide (PLA) stereocomplexes with nonequivalent molecular weights is the same as that of PLA having lower molecular weight. In addition to the PLLA/PDLA blending ratio, , which is strongly influenced by molecular weight, was considered to have a crucial effect on the lamellar curvature in the edge-on crystals of PLA stereocomplexes.