Polystyrene/TiO2 Composite Thin Films by Powder Aerosol Deposition: Film Morphology Control Through Powder Processing

Abstract

Polymer-ceramic composite (PCC) coatings combine functionality with mechanical robustness and flexibility, which is attractive for barrier coatings, membranes, or flexible electronics. Their fabrication is challenging, as conventional ceramic thin film methods make use of polymer-incompatible high-temperature sintering. Powder aerosol deposition (PAD) offers a solvent- and sinter-free avenue toward PCCs. An unresolved key question is how the preparation route of the composite powders dictates the PAD film formation and microstructure. To address this, we investigated PAD deposition of the system polystyrene (PS)-titanium dioxide (TiO2). PS particles synthesized via emulsion polymerization are combined with TiO2 particles either through dry mixing, yielding inhomogeneous powders, or through ultrasound-assisted slurry-mixing to form homogeneous powders. When deposited on polycarbonate and steel, these powders produce fundamentally different microstructures, with organized, multilayer-like films emerging from the inhomogeneous powders, and isotropic films from the homogeneous ones. These structural differences correlate with variations in crystallite size revealed by X-ray diffraction, which provided new insights into the role of internal shock absorption of the polymeric component during PAD impact. By employing a sacrificial layer, we obtained free-standing PAD-processed PCC films, which enable accurate compositional determination by thermogravimetric analysis. The fabrication of a 100 cm2 flexible coating on a PET film illustrates the scalability and potential for barrier and membrane applications. This work provides a transferable blueprint for designing hybrid thin films by PAD with tunable properties, thus bridging between polymer and ceramic processing.