Electrospray deposition of ionic liquids offers a versatile route to generate nano- and microscale architectures with tunable interfacial properties. Here, we investigate the formation and characterization of ionic liquid microdroplets (ILDs) of EMIMNTf2 deposited on undoped silicon substrates by in vacuo electrospray emission operating with several different polarity configurations. Atomic force microscopy and scanning electron microscopy reveal dome-shaped ILDs with diameters of 2–8 μm, whose size, height, and number density depend strongly on the applied extraction bias. Cation-rich ILDs exhibit the highest contact angles and lowest coalescence tendencies, reflecting the combined effects of coulombic repulsion and steric hindrance from the alkyl-substituted imidazolium cations. Nano-FTIR spectroscopy confirms uniform chemical composition across ILDs, indicating that variations in wetting behavior arise from subtle cation–anion imbalances. Dark-field scattering measurements demonstrate that ILDs act as stable broadband scatterers. These findings establish electrospray bias as a means to control droplet geometry and surface interactions, providing new opportunities for tailoring wetting, patterning, and optical properties in ionic-liquid-based materials.
DeRaad et al. (2026) studied this question.