Experimental test of the validity of the use of the n-alkanes as model compounds for polyethylene

n-Alkanes are widely used as model compounds for the dynamics of the crystalline region of polyethylene; this use relies on the assumption of the transferability of the forcefield of the n-alkanes, a stringent test of this assumption is a comparison of the dispersion curves of the n-alkanes with those of polyethylene; the only direct measurements of the dispersion curves of polyethylene are for the v₅ acoustic branch, the longitudinal acoustic mode (LAM), an in-plane skeletal mode of perdeuterated polyethylene; in the present work we have observed (by inelastic neutron scattering spectroscopy) and assigned (by the use of density functional theory calculations) the LAM modes of perdeuterated n-hexadecane in order to provide the first experimental test of the validity of the assumption.