It has been noted in the literature that the intensity autocorrelation function of polarized light scattered from aflexiblemacromolecule should in principle exhibit an initial deviation from exponential decay, even when the fluctuation wavelength is large compared to the molecular dimensions. However, it is shown here that the amplitude of the initial more rapid component rigorously vanishes in the longhyphen;wavelength limit; consequently, this effect will be extraordinarily difficult to observe experimentally for noninteracting freely flexing macromolecules. As a particular example, it is shown that the initial diffusion coefficientD00, obtained from the first cumulant of the dynamic structure factor of the Rousendash;Zimm model, actually differs somewhat from the limiting valueDinfin;prevailing at long times, but in the limitK2=0 it is the latter which characterizes theentirerelaxing amplitude, as only a vanishing amplitude is associated with former more rapid component.
展开▼
