Exploiting Reactor Geometry to Manipulate the Properties of Plasma Polymerized Acrylic Acid Films

A number of different reactor geometries can be used to deposit plasma polymer films containing specific functional groups and result in films with differing properties. Plasma polymerization was carried out in a low-pressure custom-built stainless steel T-shaped reactor using a radio frequency generator. The internal aluminium disk electrode was positioned in two different geometries: parallel and perpendicular to the samples at varying distances to demonstrate the effect of varying the electrode position and distance from the electrode on the properties of plasma polymerized acrylic acid (ppAAc) films. The surface chemistry and film thickness before and after aqueous immersion were analysed via X-ray photoelectron spectroscopy and spectroscopic ellipsometry, respectively. For a perpendicular electrode, the ppAAc film thicknesses and aqueous stability decreased while the COOH/R group concentrations increased as the distance from the electrode increased due to decreased fragmentation. For films deposited at similar distances from the electrode, those deposited with the parallel electrode were thicker, had lower COOH/R group concentrations and greater aqueous stability. These results demonstrate the necessity of having a well characterized plasma reactor to enable the deposition of films with specific properties and how reactor geometry can be exploited to tailor film properties.