Computer simulation of melting of polymer crystals

Melting processes of an n-alkane crystal (16 chains of (CH2)15: initially orthorhombic) with increasing temperature in the vacuum are simulated by a molecular dynamics method. The simulation was carried out using a kind of Lennard-Jones potential. On heating at 1 K/ps, the surface chains melt at much lower temperature than the inner chains. Details of the melting behavior are examined based on the changes in the internal rotation angles and the calculated X-ray diffraction intensity. This result indicates a new concept of surface melting of a polymer crystal.