The crystallization of ultrathin films of polylactides — Morphologies and transitions

Abstract

Poly(L-lactide) ultrathin films of thicknesses between 10 and 80 nm were crystallized between 100 and 170 °C. Four different morphologies were obtained: single crystals, hedrites, dendrites, and spherulites. Dendrites were always obtained below 20 nm due to chain diffusion limitations, whereas, at larger thicknesses, the morphology heavily depends on the crystallization temperature. The thickness-temperature morphological map led to the observation of two transition temperatures, at 115 and 145 °C. Other parameters such as the lamellar thickness, melting temperature, and dendricity of the lamellae for 15 nm thick films show significant changes at these two temperatures. Those transitions occur at the same temperatures as Regime III/Regime II, and Regime II/Regime I transitions of the Lauritzen–Hoffman crystallization theory.Key words: polylactide, ultrathin film, crystalline morphology, single crystal, dendrite, spherulite, transition temperature, regime of crystallization.