CALCULATION OF THE DYNAMIC STRUCTURE FACTOR IN POLYMER MELTS

In this work, we present calculations of the dynamic structure factor for monodisperse melts of linear polymers. Our calculations are based on a model in which a freely jointed chain encounters fluctuating obst acles whose relaxation is self-consistently determined from that of th e chain conformation. The calculation of the structure factor is relat ed to the solution of a one-dimensional random walk with dynamical dis order, which is treated within the dynamical effective medium approxim ation. This model has been applied previously to the calculation of th e self-diffusion coefficient and the mean-squared displacement of a ch ain segment. We present calculations of the structure factor over a wi de range of wave vectors, times, and entanglement molecular weights. O ur predictions are compared with calculations from the theories of Ron ca and of de Gennes, and with the experimental results for polyethylen e-butylene-2 obtained by Richter et al. from neutron spin echo measure ments. Our calculations show semiquantitative agreement with the exper imentally determined structure factors for the time range accessible t o these experiments.