Efficient electrospray deposition of surfaces smaller than the spray plume

Abstract

Electrospray deposition (ESD) uses charged droplets at the micro- and nano-scale to create a wide variety of particles and coatings. In ESD, an electrostatic force is applied to a solution, which then disperses charged droplets loaded with the materials to be deposited on a grounded target. Because the droplets carry charge, repulsive effects due to accumulation of charge in a coating (self-limiting electrospray) or “crowding” of the spray droplets can reduce the efficiency of the approach. This is especially the case when the targets are smaller than the characteristic size of the spray plume. For this reason, while many studies have presumed high efficiency in ESD, the actual measured efficiencies for small targets are much lower. Here, it is shown how architecting the local “charge landscape” can lead to ESD coatings approaching 100% deposition efficiency on both flat and microneedle array targets composed of multiple model materials, including biocompatible polymers, proteins, and bioactive small molecules. In this way, ESD can be considered a viable alternative to other conformal approaches, such as dip or inkjet coating.

Polyimide Films Manufactured Using Partially Wet Electrospray Deposition

“…Here, we take an alternate approach, through the use of a custom-designed electrospray printhead to provide focusing of the electrospray while minimizing material loss (Figure a). The dielectric shell of the printhead operates similarly to that of a dielectric focusing mask that was reported in our previous work and by other authors. ,− During electrospray, electric charge accumulates on the interior surfaces of the shell. The charge on the shell’s interior creates a repulsive charge barrier that deflects the charged particles emitted by electrospray.…”

“…However, we found that even with the focusing mask, the deposition efficiency onto the target is low (<10%) due to material being lost to neighboring grounded surfaces. Park et al have been able to greatly improve ESD efficiency on targets smaller than the spray size . Their method uses a multistep, multipolarity spray process along with a dielectric mask placed on the target.…”

“…Park et al have been able to greatly improve ESD efficiency on targets smaller than the spray size. 29 Their method uses a multistep, multipolarity spray process along with a dielectric mask placed on the target. Here, we take an alternate approach, through the use of a custom-designed electrospray printhead to provide focusing of the electrospray while minimizing material loss (Figure 1a).…”