Determination of hydrodynamic radius: a comparison of ultracentrifuge methods with dynamic light scattering

Abstract

Hydrodynamic radius, r _h, may be determined from the limiting diffusion coefficient, D ₀, from the limiting sedimentation coefficient, s ₀, or, using simple models for the concentration dependence, from the sedimentation coefficient, s, at a finite concentration. For water/AOT/heptane water-in-oil microemulsions, values of r _h determined from s are shown to agree well with those obtained from s ₀ or D ₀ determined using an analytical ultracentrifuge, and with literature values from dynamic light scattering. For several aqueous polyurethane dispersions, sedimentation velocity demonstrated the presence of small species with r _h<5 nm and medium-sized species with r _h in the range 10–17 nm, as well as much larger aggregates. For these complex dispersions, dynamic light scattering behavior was dominated by the large aggregates and analysis by the CONTIN method was not able to detect all the species present.