Surface charge accumulation and decay in electrospray printing

Abstract

In electrospray printing, the accumulation of electric charge on the target substrate plays an important role in governing the structure of the deposit. To better understand the effect of charge, we report on the use of two methods to measure the rate of charge accumulation and decay on dielectric substrates targeted with electrospray: ohmic dissipation (OhmD) and electrostatic force microscopy (EFM). The OhmD measurements were conducted on an assembly consisting of two different target materials: nylon and glass. The charge accumulation and decay were governed by the electrospray operating conditions, including spray time, flow rate, solution electrical conductivity, and the dielectric properties of the target. We found that the accumulation of charge influenced the electrospray mode in a transient way by decreasing the electric field strength between the emitter and the substrate. To complement the OhmD measurements, the charge accumulation and decay were measured at discrete spots on a silicon substrate coated with photoresist using EFM. These highly spatially resolved measurements revealed that while the electric charge was not distributed uniformly across the substrate, it still followed a similar decay trend as that obtained using the OhmD measurement. The results reported here will assist in understanding and predicting the structure of a deposit printed using electrospray.