Using dynamic light scattering to characterize mixed phase single particles levitated in a quasi-electrostatic...

Area of Science:

• Aerosol science
• Physical chemistry
• Optical physics

Background:

• Characterizing non-spherical aerosol particles is crucial for understanding atmospheric processes.
• Traditional sizing methods often struggle with irregular particle shapes.
• Electrodynamic and quasi-electrostatic balances offer controlled environments for single particle studies.

Purpose of the Study:

• To develop and validate a method for sizing non-spherical, micrometre-sized aerosol particles using Dynamic Light Scattering (DLS).
• To investigate the influence of particle shape and internal structure on DLS measurements.
• To assess the feasibility of characterizing particle dynamics within aerosol particles.

Main Methods:

• Levitation of single aerosol particles (solid salt or mixed-phase) in electrodynamic or quasi-electrostatic balances.
• Measurement of temporal intensity autocorrelation functions from far-field scattering patterns using DLS.
• Quantitative analysis of the shortest decay in autocorrelation functions, treating particles as equivalent Mie spheres.
• Attribution of intensity fluctuations to rotational Brownian motion.

Main Results:

• A quantitative method for sizing non-spherical aerosol particles based on DLS and rotational Brownian motion was established.
• The shortest decay of the autocorrelation function provides reliable particle size information.
• Deviations from Mie scattering patterns contribute to long tails in autocorrelation functions.
• Diffusional motion of inclusions within droplets is masked by rotational motion, preventing analysis.

Conclusions:

• DLS analysis of rotational Brownian motion is a viable technique for sizing non-spherical aerosol particles.
• The method allows for the characterization of both solid salt and mixed-phase aerosol particles.
• Internal particle dynamics, such as inclusion diffusion, cannot be resolved due to dominant rotational motion.