Unconventional Non‐birefringent or Birefringent Concentric Ring‐Banded Spherulites in Poly(<scp>L</scp>‐lactic acid) Thin Films

Abstract

Abstract 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 T c and thickness confinement are two factors for the unconventional concentric bands.