The Drying Kinetics and Crystallisation of Multi-Component Droplets

BARNABY MILES, Lukesh Mahato, Daniel Hardy, Spyridon Varlas, Steven P. Armes, Rachael E.H. Miles, Jonathan P. Reid, University of Bristol

     Abstract Number: 177
     Working Group: Aerosol Physics

Abstract
Understanding the drying kinetics of aerosol droplets is crucial in improving many industrial products, notably spray dried pharmaceuticals and foods, advancing climate models, and quantifying and mitigating airborne disease transmission. Changes in environmental conditions such as temperature and relative humidity (RH) influence the droplet-drying processes which impacts the final dry particle morphology. This, in turn, determines the aerodynamic and dissolution properties of the dry particles. Here, we present novel investigations into the impact of environmental factors on the evaporation and crystallisation of both multi-component aqueous inorganic salt droplets and colloidal droplets. Droplet evaporation profiles measured using an Electrodynamic balance (EDB) are compared to a model implementation for coupled heat and mass transport from solution droplets (SADKAT). Droplets dried using a falling droplet column (FDC) were collected and imaged using Scanning Electron Microscopy (SEM). Through varying the environmental relative humidity we demonstrate for both droplet systems how the evaporation rate, and hence, efflorescence time of these aerosol droplets, can be controlled. We further present details of the relationship between crystallisation time, droplet composition and resultant particle morphology.

For the inorganic salt droplets, we also show how altering the molar ratios of the component inorganic salts impacts the effect of relative humidity on the drying kinetics. Including comparisons to the drying kinetics of the constituent inorganic salts as single component droplets. We further present the composition of the dried aerosol particles as identified by SEM-EDX analysis and compare these to the compositions thermodynamically predicted by E-AIM.

For the colloidal droplet drying, we show how altering the size of the component nanoparticles in the colloidal droplet impacts the morphology of the resultant particle.