Heterodyne dynamic light scattering for the characterization of particle dispersions

Particle self-diffusivities in unimodal and bimodal aqueous dispersions are characterized by dynamic light scatter-ing (DLS) applying a heterodyne detection scheme. For unimodal dispersions close to infinite dilution, it could be evidenced that pure homodyne conditions cannot be realized, leading to an increasing underestimation of diffu-sivity with a decreasing concentration. Even for bimodal dispersions and neglecting any local oscillator field, the coherent superposition of scattered light from different particle species hinders a clear assignment of the measured signals and their evaluation for diffusivity. In this case, the impact of a cross term on the determined diffusivities cannot be neglected. The results emphasize that the use of a heterodyne detection scheme in DLS experiments is a key aspect for an accurate determination of particle diffusivities in low-concentrated unimodal and bimodal dispersions. (c) 2023 Optica Publishing Group

Automated summary

The particle self-diffusivities in unimodal and bimodal aqueous dispersions were characterized using dynamic light scattering (DLS) with a heterodyne detection scheme. The study found that for unimodal dispersions at near infinite dilution, it was not possible to achieve pure homodyne conditions, resulting in an increasing underestimation of diffusivity as the concentration decreased. Even for bimodal dispersions, the coherent superposition of scattered light from different particle species hindered the clear assignment of measured signals and their evaluation for diffusivity.