Monodisperse droplets and particles by efficient neutralization of electrosprays

Abstract

We present a new approach for micro- and nanoparticle production by in-situ charge reduction of electrospray droplets, which prevents their Coulombic instabilities and allow the efficient transport (extraction) of the particles. A unipolar ion source based on corona discharge generates a controllable ion flux of opposite polarity to the electrospray. The ions are introduced axially into the spray, while the Taylor cone is screened from the ions by an extractor ring electrode. Efficient and steady droplet discharge and extraction through an orthogonal aerosol-extraction tube was attained when the inlet of the tube was near the spray emission and the ring electrode, resulting in dramatic changes in droplets’ trajectories. The best extraction conditions (highest filter collections) were associated with the best discharging (lowest residual electrical charge) and the most globular particles. The size distributions on the particles collected on the filters were monomodal and homogeneous, with small relative standard deviations (as small as 10.6%). The use of corona ions significantly expands the range of polymer concentrations over which globular particles with monomodal size distribution can be made by electrospray.