Use of High-Flow Rate Emitters for Self-Limiting Electrospray Deposition

Electrospray deposition (ESD) stands as a versatile micro/nanocoating technique reliant on the interplay between droplet surface charge and surface tension, generating monodisperse micro/nanodroplets. The method enables the uniform deposition of thin films by incorporating dilute solutes within these droplets. In the context of ESD, one specific mode, known as self-limiting ESD (SLED), becomes evident when glassy polymers are sprayed in a volatile solvent below the polymer's glass-transition temperature (Tg). In this scenario, charge accumulation on the coating surface retards film thickness growth. Notably, the application of SLED effects has demonstrated the capability to coat 3D objects with lattice structures. While electrospray using a basic nozzle is effective at low flow rates, there's a desire to enhance flow rates for more rapid 3D target coating and broader coverage. To assess this challenge, we explore the use of two distinct emitters and their impact on the SLED effect. The first emitter is a commercial aperture-based design, with 11 virtual emitters that allow for flow rates up to 100 ml/h. This design aligns with industry standards for commercial equipment. The second emitter is a microfluidic conical emitter from literature, capable of elevating the maximum flow rate from 2 ml/h for a single nozzle to a remarkable maximum of 65 ml/h, whether used individually or divided into multiple channels to achieve higher flow rates. The results obtained from these experiments indicate that an increase in solvent vapor diminishes the self-limiting effect while expediting the deposition process. However, this reduction can be alleviated by utilizing more volatile solvents or enhancing the flow of surrounding air.