Molar Mass, Radius of Gyration and Second Virial Coefficient from new Static Light Scattering Equations for Dilute Solutions: Application to 21 (Macro)molecules

Abstract New equations for static light scattering of dilute binary solutions allow molar mass determination of macromolecules from measurements of scattered intensity ratios between solution and solvent (Ir). In contrast to the standard Carr–Zimm equations, they do not rely on the experimental absolute value of the Rayleigh ratio of a reference liquid. The picture shows a typical plot for the surfactant BRIJ72 in CH2Cl2 (MSupplier=0.359 kg mol−1). magnified image New static light scattering (SLS) equations for dilute binary solutions are derived. Contrarily to the usual SLS equations [Carr–Zimm (CZ)], the new equations have no need for the experimental absolute Rayleigh ratio of a reference liquid and solely rely on the ratio of scattered intensities of solutions and solvent. The new equations, which are based on polarizability equations, take into account the usual refractive index increment ∂n/∂ρ2 complemented by the solvent specific polarizability and a term proportional to the slope of the solution density ρ versus the solute mass concentration ρ2 (density increment). Then all the equations are applied to 21 (macro)molecules with a wide range of molar mass (0.2<M<8000 kg mol−1). On the studied dataset with M<200 kg mol−1, the new equations clearly achieve a better agreement with supplier M values. For macromolecules (M>500 kg mol−1), for which the scattered intensity is no longer independent of the scattering angle, the new equations give the same value of the radius of gyration as the CZ equation and consistent values of the second virial coefficient.