  In this study, we investigate dynamic light scattering (DLS) from both
randomly diffusing silica particles and acousto-responsive microgels in aqueous
dispersions under ultrasonic vibration. Employing high-frequency ultrasound
(US) with low amplitude ensures that the polymers remain intact without damage.
We derive theoretical expressions for the homodyne autocorrelation function,
incorporating the US term alongside the diffusion term. Subsequently, we
successfully combine US with a conventional DLS system to experimentally
characterize compact silica particles and microgels under the influence of US.
Our model allows us to extract essential parameters, including particle size,
frequency, and amplitude of particle vibration, based on the correlation
function of the scattered light intensity. The studies involving non-responsive
silica particles demonstrate that US does not disrupt size determination,
establishing them as suitable reference systems. Microgels show the same
swelling/shrinking behavior as that induced by temperature, but with
significantly faster kinetics. The findings of this study have potential
applications in various industrial and biomedical fields that benefit from the
characterization of macromolecules subjected to US.
