Both the static $(SLS) $ and dynamic $(DLS) $ light scattering techniques are used to obtain the size information from the scattered intensity, but the static radius $R_{ s}$ and the apparent hydrodynamic radius $R_{ h,app}$ are different. In this paper, the relationship between SLS and DLS is discussed using dilute water dispersions of two different homogenous spherical particles, polystyrene latexes and poly($N$-isopropylacrylamide) microgels, with a simple assumption that the hydrodynamic radius $R_{ h}$ is in proportion to the static radius $R_{ s}$, when Rayleigh-Gans-Debye approximation is valid. With the assistance of the simulated data, the apparent hydrodynamic radius $R_{ h,app}$ has been discussed. The results show that the apparent hydrodynamic radius is different with the mean hydrodynamic radius of particles and is a composite size obtained from averaging the term $\exp (-q^{ 2}D\tau) $ in the static size distribution $G(R_{ s}) $ with the weight $R_{ s}^{ 6}P(q,R_{ s}) $.
Categories: physics.chem-ph