A Spray for All Seasons: The Four Types of Electrospray Deposition

Electrospray Deposition (ESD) is a thin-film coating technique that utilizes a high voltage to atomize a flowing liquid solution into charged microdroplets. As these droplets travel toward a grounded target substrate, the solvent evaporates, allowing the solid components of the solution to deposit as a thin film. ESD regimes typically fall into one of four categories: Electrowetting, charged melt, discharged tower, and self limiting. Electrowetting, which occurs when a fluid is electrosprayed well above its melting point, results in a smooth film with reflection fringes. Charged melt refers to droplet particles landing on top of each other and building upward, with a discharged tower happening when a ‘tower’ of these particles form at the center of the spot due to rapid charge dissipation. Self-limiting is a special case where the droplet particles build upward until the film reaches a certain thickness, at which point they start to move away from the spot. Here, we present the factors that lead different materials to fall into one or another category, with the aim to modify a wide variety of solute functions to deposit in the technologically advantageous self-limiting electrospray deposition (SLED) regime.