The Drying Kinetics and Crystallization of Liquid-Liquid Phase Separated Aerosol

BARNABY MILES, Lukesh Mahato, Rachael E.H. Miles, Jonathan P. Reid, University of Bristol

     Abstract Number: 16
     Working Group: Aerosol Physics

Abstract
Liquid-liquid phase separation (LLPS) is a process that can occur in aerosol droplets containing a mixture of organic and inorganic components below a given relative humidity. This phase separation can lead to changes in the aerosol droplets physiochemical properties, such as its ability to act as a CCN seed, the heterogeneous reactivity and it’s optical properties. There has been previous work looking at LLPS for a number of different systems, with investigations into the RH at which LLPS occurs and the mechanism that causes the separation e.g. spinodal decomposition or nucleation and growth (D. Stewart et al. (2015), S. Ma et al. (2021), J. Choczynski (2024)). There has not yet been any investigations into the effects of RH and droplet composition on the physiochemical properties of the resultant ‘dried’ particles for aerosols that undergo LLPS.

Here, we present novel investigations into the impact of RH, organic: inorganic (O:I) component ratio, and organic component chain length, on the evaporation and crystallization processes of aerosol droplets that undergo LLPS. Droplet evaporation profiles and phase functions were measured using an Electrodynamic balance (EDB) and compared to a model implementation for coupled heat and mass transport from solution droplets (SADKAT) (Robinson and Hardy (2022)). 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 the effect of evaporation rate on the phase separation behavior (e.g. the time taken for the droplets to undergo LLPS, and the radius of the droplet when LLPS occurs). We further present details of the relationship between O:I ratio, organic component chain length, phase separation behavior, crystallization behavior and resultant particle morphology.