Dynamics of submicron microsphere suspensions observed by dynamic ultrasound scattering techniques in the frequency-domain

Dynamic ultrasound scattering (DSS) techniques have been employed in order to evaluate the dynamics and size of submicron-particles. In addition to the fact that the ultrasound-based techniques could be applied to optically turbid systems, a novel method called frequency-domain DSS allowed us to investigate complex fluid dynamics involving both thermal diffusion and settling of microspheres by recording the time-correlation function at the corresponding spatial length scales. While the particle sizing was successful for silica and polystyrene particles with the hydrodynamics radii down to 100 nm, which was 20 times smaller than the minimal detectable size in the previous DSS studies, coupling of diffusion and sedimentation modes was observed. Since it enables us to quantitatively evaluate the particle motions at the individual scanning windows by a single acquisition, diffusion and sedimentation of submicron particles were simultaneously analyzed at the corresponding scattering vectors where the contribution from sedimentation was neutralized by the density matching. (C) 2014 AIP Publishing LLC.