Viscoelastic Properties of Electrospray-Deposited Polymer Shells via Quartz Crystal Microbalance With Dissipation (QCM-D)

Abstract

Multilayer polymer films are extensively used in multiphase separation. Electrospray deposition (ESD) is an important technique for fabricating such films with tunable morphology. Viscoelastic properties of polystyrene (PS) nanoshell coatings produced by ESD on gold and spin-coated PS surfaces are evaluated using Quartz Crystal Microbalance with Dissipation (QCM-D). The thickness of PS films on gold increases with flow rate from ∼200 nm at 0.5 to ∼400 nm at 1.5 mL h⁻¹, accompanied by an order-of-magnitude increase in dissipation due to larger particle sizes from shorter droplet flight times. This effect is absent on spin–coated PS films, suggesting the onset of the self-limiting effect of charges. Although the shear moduli for ESD films calculated from Voigt models 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) × 10³ m⁻¹, due to shell–shell and shell–substrate interactions. These are novel results related to the interparticle friction obtained using QCM-D for the first time. This work demonstrates  that mechanical properties of particulate viscoelastic films with potential applications in high surface area sensors, such as size-selective membranes for protein or electrolyte adsorption, can be evalauted by QCM-D with nanograms of material.