Self-limiting electrospray deposition for the surface modification of additively manufactured parts

Abstract

Electrospray deposition (ESD) is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target substrate, depositing the solution solids. Our previous research investigated the conditions necessary to minimize charge dissipation and deposit a thickness-limited film that grows in area over time through self-limiting electrospray deposition (SLED). Such sprays possess the ability to conformally coat complex three-dimensional objects without changing the location of the spray needle or orientation of the object. This makes them ideally suited for the post-processing of materials fabricated through additive manufacturing (AM), opening a paradigm of independent bulk and surface functionality. Having demonstrated three-dimensional coating with film thickness in the range of 1-50 µm on a variety of conductive objects, in this study we employed model substrates to quantitatively study the technique’s limits with regard to geometry and scale. Specifically, we examined the effectiveness of thickness-limited ESD for coating recessed features with gaps ranging from 50 µm to 1 cm, as well as the ability to coat surfaces hidden from the line-of-sight of the spray needle. This was then extended to the coating of hydrogel structures printed by AM, demonstrating that coating could be conducted even into the body of the structures as a means to create hydrophobic surfaces without affecting the absorption-driven humidity response.