Development of a standard method for nanoparticle sizing by using the angular dependence of dynamic light scattering.

A standard method for nanoparticle sizing based on the angular dependence of dynamic light scattering was developed. The dependences of the diffusion coefficients for aqueous suspensions of polystyrene latex on the concentration and scattering angle were accurately measured by using a high-resolution dynamic light-scattering instrument. Precise measurements of the short-time correlation function at seven scattering angles and five concentrations were made for suspensions of polystyrene latex particles with diameters from 30 to 100 nm. The apparent diffusion coefficients obtained at various angles and concentrations showed properties characteristic of polystyrene latex particles with electrostatic interactions. A simulation was used to calculate a dynamic structure factor representing the long-range interactions between particles. Extrapolations to infinite dilution and to low angles gave accurate particle sizes by eliminating the effects of long-range interactions. The resulting particle sizes were consistent with those measured by using a differential mobility analyzer and those obtained by pulsed-field gradient nuclear magnetic resonance measurements.