Interface-Mediated Electrospray Deposition: Understanding the Efficacy of Material Delivery using Substrate Focusing Methods

The field-driven nature of electrospray gives it the unique ability to deposit conformal coatings onto a wide range of substrates. The microstructure of these thin films tend to be limited by the spray parameters, such as voltage, suspension volatility, and particle size. Instead of depositing particles to a dry substrate directly, we introduce a water-air interface as the target in order to "reconfigure" the microstructure before the liquid completely evaporates. In this work, we employ a range of thin (0.2 - 1.0 mm) dielectric masks attached to a conductive substrate serving two functions: 1. to define the position of the target droplet contact line and 2. to focus the electrosprayed material towards the waiter-air interface. We primarily consider the case of spherical cap droplets with r = 0.5 or 1 mm, as these are close to the resolution limit of our additively manufactured masks. In addition to the 3D printed ABS/PLA masks we tested FR4 as a focusing material, and observed a reduction in material delivery efficiency. We believe this may be caused by increased charge mobility on the surface of the mask, which would allow the positive electrostatic charge deposited by electrospray to dissipate or redistribute faster than expected. Finally, we can also evaluate the effect of focusing material thickness. By understanding the relationship between mask geometry, material properties, and deposition efficacy, we can find the optimal substrate modifications for our system.