While a negative value suggests that aggregation is likely, a positive value reflects good particle-solvent interactions, and therefore stability. In the case of protein or nanoparticle dispersions, the 2 nd virial coefficient can be used to predict aggregation in different solutes. However, the exact interpretation of the thermodynamic term differs for different sample groups. In general, if the second virial coefficient is positive, particle-solvent interactions are energetically favorable, while if the term is negative, particle-particle interactions are favored. This parameter is a thermodynamic term, which describes the particle-solvent and particle-particle interactions. īesides the molecular mass, the method of static light scattering also determines the second virial coefficient (A 2). If the radius of gyration is of interest, an X-ray source is required (see also small-angle X-ray scattering, SAXS). As the scattering intensity is uniform around the particles, the radius of gyration cannot be determined using laser-based instruments. This approach is inherent to the static light-scattering method, which is explained in detail below. In this case, the evaluation is performed through the Debye plot which marks Kc/ΔR over the concentration (s. The connection between scattering intensity and molecular mass is described in the Debye-Zimm equation, which is the theoretical basis for static light-scattering measurements: As the intensity of scattered light is proportional to the radius of the particle, this information can be used to draw a conclusion about the size of the particles in the dispersion. When light comes in contact with any particle, it is forced to deviate from a straight trajectory.

Light scattering intensity equation