Chemical structure and morphology of thin bilayer and composite organosilicon and fluorocarbon microwave plasma polymer films

Abstract

A microwave plasma polymerisation set-up with a linear plasma source was used to deposit thin bilayer and nanocomposite films of fluorocarbon and organosilicon plasma polymers. Hexamethyldisilane (HMDS) and heptadecafluoro-1-decen (HDFD) were used as monomers. The chemical structure was measured by means of Fourier Transformation Infrared Reflection Absorption Spectroscopy (IRRAS), X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy measurements provided information about the surface morphology. The surface chemistry and surface morphology were correlated with the surface energy as calculated by contact angle measurements. The plasma polymer deposited from a gas mixture of heptadecafluoro-1-decen fluorocarbon and hexamethyldisilane consists of rough cauliflower, polysiloxane-like structures embedded in a smooth fluorocarbon matrix. Moreover, co-polymeric species which are likely to exist at the interface between the two phases in the film were observed. The bilayer system that consisted of a rough interfacial organosilane film coated with a smooth fluorocarbon layer, showed the lowest apparent surface energy and a high water contact angle as the result of both high surface roughness and a high concentration of surface CF 2 groups.