In-situ hot stage atomic force microscopy study of poly(ε-caprolactone) crystal growth in ultrathin films

Morphologies, growth rates, and melting of isothermally crystallized ultrathin (200-1 nm) poly(e-caprolactone) (PCL) films have been investigated in real time by atomic force microscopy. The flat-on orientation of the lamellar crystals relative to the substrate was determined by electron diffraction. The truncated lozenge-shaped PCL crystals observed at low undercooling become distorted for films of thicknesses equal to or thinner than the lamellar thickness, which depends on the crystallization temperature but not on the initial film thickness. The melting behavior of distorted crystals differs from that of undistorted ones, and their growth is slower and nonlinear. The crystal growth rate decreases greatly with the film thickness. All these observations are discussed in terms of the diffusion of the polymer chains from the melt to the crystal growth front.