Small-angle neutron scattering and dynamic light scattering from a polyelectrolyte solution: DNA

Static and dynamic properties of a DNA fragment of molecular weight 316 800 (contour length 1632 Angstrom) in semidilute solutions are studied by small-angle neutron scattering (SANS) and static (SLS) and dynamic light scattering(DLS). SANS experiments in a solution with DNA concentration C-p = 42 mg mL(-1) were performed as functions of added salt concentration C-s and temperature. The resulting plot of scattering intensity I(q) versus scattering wavevector magnitude q shows the existence of a broad peak whose position is independent of both C-s and temperature. Additionally, an "upturn" in the small scattering vector length range (q < 0.01 Angstrom(-1)) is observed and is temperature-independent. The DLS time correlation function of the same sample shows the two relaxation modes that have previously been observed in DNA and other polyelectrolyte solutions as well as an additional "ultra" slow mode whose corresponding size is much larger than various correlation lengths that may be deduced from SLS experiments and the upturn in the SANS data for small q values.