Light scattering characterization of lignosulfonate structure in saline solutions

Abstract

The solution behavior and molecular conformation of sodium lignosulfonates (NaLS) in saline solution has been studied by means of static and dynamic light scattering (LS stat and LS dyn ). Results show that the salt content must be larger to eliminate the slow mode in LS dyn 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 cm 2 s -1 , and the corresponding M w = 1.7 × 10 5 g mol -1 .

A Critical Review of the Physicochemical Properties of Lignosulfonates: Chemical Structure and Behavior in Aqueous Solution, at Surfaces and Interfaces

“…Two schematics of the proposed mechanisms during lignosulfonate aggregation are shown in Figure 7. It should be noted that the geometrical representation for individual lignosulfonate molecules used by Vainio et al [85], i.e., flat cuboid-like particles, is not consistent with the spheroidal conformation reported by other authors [4,21,115].…”

“…Two schematics of the proposed mechanisms during lignosulfonate aggregation are shown in Figure 7. It should be noted that the geometrical representation for individual lignosulfonate molecules used by Vainio et al [85], i.e., flat cuboid-like particles, is not consistent with the spheroidal conformation reported by other authors [4,21,115]. Lignosulfonate aggregation can be induced by increasing lignosulfonate or salt concentration, by adding alcohol, by reducing pH, and by increasing the temperature [82,85,123].…”

“…At high molecular weight, the shape was better approximated by an "elongated or fully stretched shape" [21]. The conformation of lignosulfonates aqueous solution may indeed be better described as oblate spheroid shape [83,115].…”

“…Surfaces 2020, 3 FOR PEER REVIEW 9 The conformation of lignosulfonates aqueous solution may indeed be better described as oblate spheroid shape [83,115]. At low salinity and low lignosulfonate concentration, the lignosulfonate molecule is expanded due to electrostatic repulsion between the anionic groups [116].…”

Fast track for quantitative isolation of lignosulfonates from spent sulfite liquors

“…Many attempts have been made to determine the molecular weight of lignosulfonates; [38][39][40] however, some fundamental obstacles, such as solubility, aggregation, dispersity, uorescence, and absence of appropriate lignin standards for GPC column calibration, have prevented an accurate determination of their molar mass. 3,40,41 In this study, GPC was applied to determine whether different isolation protocols result in comparable molar mass distributions (MMD).…”