Large-Scale Electrospray Ionization Methods for Nanocoating Application

A scalable nano-coating process is needed that can be applied at atmospheric temperatures and pressures with low waste. This would enable the efficient production of advanced thin-film materials from solar cells to super-hydrophobic surfaces. Unfortunately, current methods for producing nanoparticle or nano-structured macromolecular coatings often require substrate immersion, specific atmospheres, and/or long growth times. One potential technique to overcome these challenges would be to use electrospray ionization (ESI) to first disperse large numbers of nanoparticles or polymers in air at standard conditions, and then deposit these on a substrate. ESI is a relatively mature technology, and although it has been developed largely for processing microliter volumes in mass spectrometry, it is believed that the fundamental science can be scaled up. This work presents a model for an ESI deposition method. It combines scaling laws for charged jets with spray and fission models to capture relevant charge, spray, fission, and evaporation phenomena. The developed model is shown to be very simple and efficient while still matching published experimental results. Using the model, current ESI techniques are compared such as NanoESI and Flow-Focusing ESI. A significant technological challenge to ESI deposition is discovered to be the trapping of the majority of the solute in a few primary droplets. Different solutions to this challenge are examined and used to define the direction for future work.