Characterization of highly conducting ionic liquid (EMI-BF4)mEMIn+ nanoclusters injected into dielectrics to produce compound electrosprays

Abstract

Electrospraying of dielectric liquids presents unique challenges compared to conducting liquids, as it requires external charge injection. This manuscript further explores the Charge Injection Atomization (CIA) technique, which employs two concentric capillaries to create a compound electrospray. The inner liquid is an ionic liquid (IL), which injects nanodrops and perhaps also ions into the dielectric. The evaporation of the dielectric liberates these charged particles into the gas phase, where they are analyzed with a Differential Mobility Analyzer (DMA). The mobility spectra show very narrow peaks of high mobility (corresponding to ions) and broader, lower mobility peaks representing IL nanodrops. In this work, the effects of both the ionic liquid and dielectric flow rates on droplet diameter and charge are thoroughly studied. Through a simple assumption that the mobility of the droplets agrees with Stokes-Millikan and the condition that the droplets are spherical of known density, the diameter and mass over charge, $m/z$ are determined, revealing average $m/z$ values ranging from 7 to 90 kDa and diameters from 3 to 35 nm. The charge density of the droplets seems to suggest that they are charged to a fraction between 50 and 100% of the Rayleigh limit and are affected mostly by the ionic liquid flow rate as expected. Given the broad interest of IL, the controlled size production of nanoclusters in dielectrics can have important implications in synthesis and catalysis, polymer chemistry, electrochemistry, microemulsions and biotechnology.