Light scattering characterization of lignosulfonate structure in saline solutions

The solution behavior and molecular conformation of sodium lignosulfonates (NaLS) in saline solution has been studied by means of static and dynamic light scattering (LSstat and LSdyn). Results show that the salt content must be larger to eliminate the slow mode in LSdyn analysis of NaLS than that of the theory, and this discrepancy can only be explained by a modified microgel model. The higher salt amount is needed for the formation of a strong ionic gradient field between surface and the inner part of NaLS, which forces counter ions to penetrate into the inner part of NaLS to screen the small amount of charges. The NaLS single molecular shape can be described by an oblate spheroid based on the absolute molecular weight M w and diffusion coefficients D. The best fitting result is semiaxis a=1.6 nm and axial ratio r=3.5, D=5.73×10-7 cm2 s-1, and the corresponding M w=1.7×105 g mol-1.