Electrospray deposit structure of nanoparticle suspensions

Electrospray atomization has unique capabilities for deploying colloidal suspensions to create nanoparticle films and coatings. This technique can deliver precise quantities of particles in a dry state to a target substrate and overcomes many limitations of other printing and coating technologies. Since the structure of a nanoparticle layer governs its functionalities, it is essential to understand the relationship between the key operating parameters and the macro- and microstructure of an electrospray deposit. We investigated the role of three key parameters on the deposit structure: electrospray time, the target substrate electrical properties, and the polydispersity of the colloidal suspension. The macrostructure of the nanoparticle deposits was similar for all spray times and substrates. In particular, the deposited particles segregate to the center and edge of a deposit, leaving a depletion region in between. We speculate that the mutual Coulombic forces due to the space charge inside the plume play a key role in governing the trajectory of the nanoparticles and the ensuing deposit morphology. Since particles emitted by electrospray are highly charged, the microstructure of a deposit was strongly influenced by the electrical conductivity of the target substrate. By maintaining a net charge, particles deposited on to a dielectric substrate could influence the deposition of subsequent in-flight particles, which opens new routes for exerting control over the deposit structure.