The thickness of adsorbed polyelectrolyte layers on oppositely charged particles can be
measured by dynamic light scattering (DLS) with a precision of fractions of a nanometer. However, such data
can be only reliably obtained when effects of particle aggregation are carefully eliminated by working at
low particle number concentrations. In order to achieve a sufficient light scattering intensity at the same time,
the size of colloidal particles must be chosen relatively large. We find that such measurements are best carried
out with latex particles in the range of diameters of 150-300 nm. The precision of the measurement can be
further enhanced with multiangle DLS. The thickness of adsorbed polyelectrolyte layers on oppositely
charged particles is normally below 10 nm. At low ionic strengths, a typical thickness is merely 1-2 nm, while
at higher ionic strengths one observes thicknesses between 6 and 9 nm. The transition between these two
regimes occurs at ionic strengths 0.01-0.05 M. These observations were made with various highly charged
cationic and anionic polyelectrolytes and can be considered as quite generic.
