Controlling the nanostructure and stability of a-C:H:N plasma polymers

Plasma polymer films might exhibit nanostructures when deposited under particular deposition conditions. While mainly mild plasma conditions favor the growth of nanostructures, this work investigates the formation of nanopores in amino-containing hydrocarbon (a-C:H:N) films that show mechanical stability against abrasion and thus strongly enhance the permanence of chemically attached long-chain fluorocarbon molecules. By examining gas phase and surface processes during film growth, it is assumed that the rather large interconnected voids (> 3 nm pore sizes) are caused by incorporation of terminal amino groups as well as ion-induced effects enhancing surface mobility and cross-linking. Rather large molecules can thus penetrate the plasma polymer films and can be bound to functional groups throughout the film thickness. Using for example long-chain fluorocarbon molecules, the attached monolayer is thus protected, while its hydrophobic CF3 end-groups align to the outside resulting in high oil repellence grades. While amino-rich plasma polymers undergo severe aging effects, the films tend to stabilize when their amino groups have reacted with further chemical molecules.