Analysis of the low-temperature specific heat in polyethylene

The low-temperature specific heats of polyethylene polymers with different degrees of crystallinity have been reproduced by considering a linear overlap of the contributions from both the crystalline and the amorphous phases characterizing the polymer. The excess specific heat over that provided from the Debye theory is assumed to be due to the amorphous phase and has been described by an empirical phonon-fracton density of vibrational states. A comparison between the 'fragility' of the amorphous fraction of the polymers and the excess specific heat has been tried. Within the range of crystallinities explored, no correlation has been found between the fragility and the density of additional low-energy vibrations.