Crystal and multiple melting behaviors of PCL lamellae in ultrathin films

• The transformation of crystal growth process was discussed.
• The multiple melting of PCL films was due to two different lamellar structures.
• The crystal temperature has obvious influences on the crystal structure.

In this paper, isothermal crystallization at different temperatures and multiple melting of four molecular weights (MW) PCL ultrathin films were investigated by using Atomic Force Microscopy (AFM). The results showed that: two different crystal structures, Flat-on and Edge-on lamellae, were simultaneously formed in PCL ultrathin films when the Tc lower than 30 °C. During the heating process, Edge-on lamellae was melted firstly. This demonstrated that the multiple melting behavior of PCL in ultrathin films was caused by the two different lamellar structures. With the increase of MW, or with the decrease of Tc, PCL chains in ultrathin films changed from Flat-on to Edge-on, and the controlled factors of growth process in ultrathin films transformed from surface nucleation-limited (NL) to melt diffusion-limited (DL).