Understanding Plasma–Liquid Interactions and Plasma-Induced Free-Radical Polymerisation in Liquid-Assisted Atmospheric Plasma Polymerisation—Application to Antioxidant Coating

Abstract

Liquid-assisted atmospheric plasma polymerisation (LA-APP) enables the rapid curing of liquid monomer layers into polymer thin films without chemical initiators. This study investigates the plasma-induced free-radical polymerisation of trimethylolpropane propoxylate triacrylate (TMPTA-PO) to elucidate the role of liquid monomer layer thickness and plasma exposure on curing efficiency. Static and dynamic deposition approaches revealed a thickness-dependent diffusion depth of plasma-generated reactive species, with FTIR spectroscopy quantifying a high conversion degree for thin layers and incomplete bulk curing for thicker layers. The approach was implemented to embed rosmarinic acid as a natural antioxidant, yielding thin films with preserved antioxidant activity. These findings provide fundamental insight into plasma–liquid interactions and guidelines for controlled fabrication of multifunctional coatings.