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Keywords:

  • crystallization;
  • autophobic dewetting;
  • poly(ε-caprolactone)-b-poly(L-lactide);
  • ultrathin film

Abstract

We have investigated the crystallization and morphological behaviors of poly(ε-caprolactone)-b-poly(L-lactide) (PCL-b-PLLA) in its autophobic dewetted ultrathin films (∼11 nm) using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The autophobic dewetting process creates a well defined film geometry containing an extremely thin wetting layer (∼4.5 nm) with densely distributed micrometer droplets atop, which restricts the primary nucleation process to occurring only in the droplets. In addition to the normally encountered flat-on lamellae, the growth of edge-on lamellae in such a thin wetting layer has been observed on both of two crystallization paths. In thermal crystallization, flat-on lamellae are favored at small supercoolings while edge-on lamellae appear at very large supercoolings both in the droplets and the wetting layer. For cold crystallization, the edge-on lamellae can form easily in the droplets and grow into the wetting layer even at very small supercoolings. These observations are explained on the basis that the nucleation and lamellar orientation are strongly affected by the film geometry, the crystallization paths, and the applied supercoolings.