Process parameters for fast production of ultra-thin polymer film with electrospray deposition under ambient conditions.

Poly(vinylidene fluoride) films between 60 and 120nm have been prepared with electrostatic spray deposition (ESD) in 25-45s. The films are robust and exhibit a strong adhesion to the substrate surface. The important electrospray parameters for ultra-thin film formation are droplet size, initial polymer concentration, shear rate at impact, and volume flux. The latter can be understood as a measure for the solvent balance between deposition and evaporation; it affects overall film quality. The droplet size determines the minimum film thickness at which continuous film forms without voids. Polymer concentration affects thin-film smoothness and below a fixed concentration threshold, films cease to appear. For the very first droplets, wetting behavior on the substrate is most important. Subsequently, shear rate determines how voids are filled up and it determines final film smoothness. In addition to the electrospray conditions, substrates that favor wetting and have a capability to conduct charges away from the surface contribute to the formation of well-defined, ultra-thin films.