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submitted on 24.10.2019 and posted on 28.10.2019by Dylan A. Kovacevich, Lin Lei, Daehoon Han, Christianna Kutznetsova, Howon Lee, Jonathan Singer
(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.