Reconciling Dynamic and Structural Scattering for Charged Nanoassemblies

Electrostatic interactions can bias hydrodynamic sizes inferred from dynamic light scattering (DLS), driving persistent discrepancies with structural methods. This disagreement is particularly well documented for solutions of charged nanoassemblies, with DLS consistently underestimating hydrodynamic sizes for systems with strong interactions. We quantify this for solutions of sodium dodecyl sulfate (SDS) micelles using multi-angle DLS across a wide range of NaCl concentrations to tune intermicellar interactions. We analyze the results in a collective-diffusion framework where DLS radii are brought into agreement with independent measurements from small-angle X-ray scattering (SAXS) and literature. This is done using a generalized Stokes-Einstein formalism in which DLS sizes are "corrected" using appropriate structure factor and hydrodynamic contributions. Across SDS concentrations and ionic strengths, the salt dependence of DLS radii matches collective-diffusion predictions, indicating that much of the DLS–SAXS mismatch indeed arises from interparticle correlations rather than true morphological changes. These results enable more reliable interpretation of dynamic scattering in charged formulations, improving size and dispersity estimates for electrostatically crowded systems.