The drying of solution droplets, and the crystallisation to form particles, is a problem relevant to a range of industries such as spray-drying, respiratory drug-delivery, climate modelling and crop-spraying. This work aims to understand the drying kinetics and crystallization behaviour of single aqueous aerosol droplets under a range of different conditions, and to develop models that consider the transport mechanisms occurring in the droplets leading to particle formation.

Single aerosol droplets containing salt solutions (e.g. NaCl, NaNO3) are levitated in an electrodynamic balance; the radius of an evaporating droplet is measured and the time that crystallisation occurs is determined using light scattering techniques. A model is presented that tracks the interplay between diffusion within the droplet and the receding interface as it dries, to show the build-up of concentration gradients within the droplet and to ultimately predict when crystallisation will occur.

This work will be useful in developing models for spray-drying, so that the resulting size and morphology of products can be predicted and controlled.