The prediction of size and charge of particles formed from evaporation of charged droplets generated in an electrospray system

Abstract

Electrospray systems are an effective methodology for generating uniform submicrometer sized charged droplets, initially containing a dissolved solute or nanoparticle inclusions, producing particles from the droplets. In this work, we develop a model for charged droplet drying to predict the final size and resultant charge of the particles. The model accounts for solvent evaporation, solute/nanoparticle diffusion, the collision and aggregation of nanoparticles, coulombic fission and ion evaporation processes. The competition among these subprocesses determines the final size and charge. The model equations are cast into nondimensional forms for generalization. The governing dimensionless parameters are derived and their influences on the final particle size and charge are investigated numerically. The most important parameters are the non-dimensional characteristic diffusion time, non-dimensional characteristic coagulation time, non-dimensional flow rate and coulombic fission related loss. An analytical solution is obtained in the case of slow drying.