Unconventional concentric up-and-down bands, differing from the conventional bright- extinction or blue/orange bands in other polymers, in poly(L-lactic acid) are found via controlled thin films. Non-birefringent and birefringent concentric banded spherulites are obtained from 350-400 nm and 1800-2000 nm film thicknesses, respectively. Non-birefringent concentric ring-banded spherulites are arranged only by flat-on lamellae; in contrast, complex combinations of flat-on, edge-on, and round-shaped lamellae in four transitional zones are present within a single band in the thicker films of birefringent, concentric, ring-banded spherulites. Interband is an optically extinction crevice that segregates two neighboring bands. Unique lamellar arrangements at specific Tc and thickness confinement are two factors for the unconventional concentric bands. The film thickness and different lamellar arrangements are proven to induce the formation of non-birefringent or birefringent concentric ring-banded spherulites in thin poly(L-lactic acid) (PLLA) spin-cast films (about 350-400 nm or 1800-2000 nm).
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Organic Chemistry
- Polymers and Plastics
- Materials Chemistry