Self-limiting electrospray deposition on polymer masks

Electrospray deposition (ESD) can produce monodisperse generations of droplets down to hundreds of nanometers in diameter by applying high voltage to liquids flowing through capillaries. This deposition method has been combined with insulated stencil masks for fabricating micro patterns by spraying nanoparticles, polymers, or biomaterials. To optimize the fabrication process for micro coatings, a self-limiting electrospray deposition (SLED) method has recently been developed. Here we combine SLED with a pre-existing polymer film to study the fundamental behavior of this process in a bilayer geometry. SLED has been observed when insulating materials are sprayed onto conductive substrates. A thickness-limited film will occur when charge accumulates and repels the arrival of additional charged droplets. In this study, polystyrene (PS) and Parylene C thin films of varying thicknesses are utilized as insulated spraying substrates. Polyvinypyrrolidone (PVP), a thermoplastic polymer is sprayed to investigate the SLED behavior on the pre-deposited insulating films. Moreover, to examine the effects of in-plane confinement on the spray, a microhole array patterned onto the PS thin film by focused laser spike (FLaSk) dewetting was sprayed with PVP in the SLED mode.