INFLUENCE OF STIFFNESS ON THE DYNAMICS OF MACROMOLECULES IN A MELT

Analytical expressions are derived for the incoherent and coherent dyn amic structure factor of macromolecules in a melt. In particular, the influence of chain stiffness on these quantities is investigated. For scattering vectors q<pi p/2, where 1/2p is the persistence length of t he macromolecules, the well known results for the Rouse model are repr oduced. However, in the scattering vector range q>pi p/2 the incoheren t dynamic structure factor is shown to be a universal function of only the combination q(8/3)tp(1/3), reflecting the strong influence of the local chain stiffness on dynamical properties at small length scales. Moreover, the q dependence of both the full width at half maximum of the Fourier transformed incoherent dynamic structure factor and the in itial decay rate of the coherent dynamic structure factor are calculat ed. The comparison of the theoretical results with quasielastic neutro n scattering experiments of different polymers exhibits good agreement . (C) 1997 American Institute of Physics.