Entropically Induced Euler Buckling Instabilities in Polymer Crystals

Abstract

Molecular simulations show that heating crystalline polyethylene leads to an entropically induced Euler buckling instability, associated with the softening of the long wavelength transverse acoustic vibrational modes propagating along the chain axis. This entropic effect is augmented by axial compressive stress, leading to a decrease in the instability temperature with applied stress. For zero or low compressive stresses, the instability will occur above the melting temperature and impose a maximum temperature for the superheated crystal; for high compressive stresses, the instability will occur below the melting temperature and trigger a transition to another solid structure.