DYNAMIC SCATTERING FROM SOLUTIONS OF SEMIFLEXIBLE POLYMERS

The dynamic structure factor of semiflexible polymers in solution is d erived from the wormlike chain model. Special attention is paid to the rigid constraint of an inextensible contour and to he hydrodynamic in teractions. For the cases of dilute and semidilute solutions exact exp ressions for the initial slope are obtained. When the hydrodynamic int eraction is treated on the level of a renormalized friction coefficien t, the decay of the structure factor due to the structural relaxation obeys a stretched exponential law in agreement with experiments on act in. We show how the characteristic parameters of the system (the persi stence length l(p), the lateral diameter a of the molecules, and the m esh size xi(m) of the network) are readily determined by a single scat tering experiment with scattering wavelength lambda obeying a much les s than lambda much less than l(p) and lambda < xi(m). We also find an exact explicit expression for the effective (wave-vector-dependent) dy namic exponent z(k)<3 for semiflexible polymers and thus an enlighteni ng explanation for a longstanding puzzle in polymer physics.