Dynamic light scattering investigation of single levitated micrometre-sized droplets containing spherical nanoparticles

•Single levitating droplets are investigated with dynamic light scattering technique.•Autocorrelation function reflects the evolution of the microdroplet of dispersion.•The rotational Brownian motion of the aggregate in the trap can be detected.•The autocorrelation functions are different from those for the dispersion in bulk. We applied the dynamic light scattering (DLS) technique for studying single microdroplets of dispersions of SiO2 and TiO2 nanoparticles. The evaporating microdroplets were levitating in an electrodynamic quadrupole trap. Exponentially decaying autocorrelation functions (ACFs) were obtained for the light scattered by evaporating microdroplets as well as for microaggregates of nanoparticles formed at the end of the evaporation process. It was found that the temporal variation of the ACF generally reflects the evolution of the microdroplet of dispersion. At the initial stage of the evaporation, apart from the optical morphology resonances of the droplet (dielectric sphere), it was possible to identify the characteristic times corresponding to the Brownian motion of the dispersed nanoparticles. At the end of evolution, when the drying microdroplet transforms into a (non-rigid) microaggregate, the Brownian motion of the dispersed nanoparticles was masked by the rotational Brownian motion of the microaggregate as a whole.