Secondary bias-assisted high-throughput electrospray for uniform and self-limiting coatings at elevated flow rates

Self-limiting electrospray deposition (SLED) enables conformal coatings by allowing surface charge buildup to reshape local electric fields, redirecting spray toward uncoated regions. This requires droplets to travel non-inertially, so they respond to near-field electric changes, which break down at high flow rates when droplet inertia dominates. Here, we demonstrate that high-flow emitters maintain SLED behavior up to ∼ 5 mL/h per tip, an order of magnitude increase in throughput, producing uniform ∼ 4–5 μ m PMMA films and conformal coatings on 3D objects. Beyond this, anisotropic deposition arises due to high Stokes numbers. Applying a same-polarity secondary bias softens droplet landing, mitigating inertial overdeposition and restoring uniform deposition at rates up to 12 mL/h. Simulations further show that increased air pressure can achieve similar effects. These results frame SLED as a Stokes-number-dependent regime and offer a scalable strategy to extend conformal electrospray coatings to large areas, complex geometries, and industrially relevant throughputs. • Conformality in electrospray coatings prevented by droplet inertia. • Inertial-to-electrostatic transition identified near 5 mL/h flow rate. • Secondary bias reduces droplet inertia and improves coating uniformity. • Uniform coatings achieved on 3D structures at high deposition rates up to 12 mL/h.