Viscoelastic properties of electrospray-deposited polymer shells via quartz crystal microbalance with dissipation (QCM-D)

Viscoelastic properties of polymer nanoshell coatings fabricated by electrospray deposition (ESD), on gold-coated quartz crystals and spin-coated polystyrene (PS) surfaces, were evaluated using Quartz Crystal Microbalance with Dissipation (QCM-D). For PS particles on gold, as ESD flow rate increases from 0.5 to 1.5 mL/h, film thickness increases from ~200 to 400 nm, while dissipation increases by an order of magnitude. This is attributed to larger particle sizes resulting from shorter droplet flight times during ESD. Absence of this effect on spin-coated PS films suggest complex interfacial interactions between ESD PS shells and spin-coated PS films. Shear moduli for ESD coatings on gold are found to be virtually independent of flowrate (i.e. particle size) and are consistent with literature on expanded polystyrene foams. While the QCM-D modulus of the spray coated film is only 0.08-0.20% of the bulk PS modulus, the stiffness ratio of spray coated PS to a single shell is 5.00 - 13.3 x 103 m-1, due the more rigid response arising from shell-shell and shell-substrate interactions. These results underscore QCM-D, with nanograms of material, has the potential to predict the mechanical properties of particulate viscoelastic films suitable for high surface area sensor applications such as size-selective membranes relevant to protein or electrolyte adsorption.